Rules for adding and subtracting two-digit numbers. How to explain to a child the subtraction and addition of two-digit numbers. But I will say with respect -
Have you ever been amazed by people who easily add and multiply three-digit numbers in their heads or instantly call the root of 729?
In fact, it is not as difficult as it seems, just here, as in any skill, you need knowledge of the technique and regular training. Well, training depends only on you, and we will now analyze the technique.
Let's start with adding two-digit numbers.
Let us need to calculate 37 + 85 + 29 + 42 . To do this, first add all the tens: 3 + 8 + 2 + 4. Note that 8 + 2 = 10, 3 + 4 = 7, together 17. Remember. Now add the units: 7 + 5 + 9 + 2 = 23.
17 tens is 170. 170 + 23 = 193. As you can see, this is faster than adding 37 and 85, then adding 29, and so on.
By the way, the same can be done if we add three-digit numbers.
For example: 228 + 39 + 485 + 91.
Adding tens:
22 + 3 + 48 + 9 = (22 + 48) + (3 + 9) = 70 + 12 = 82.
Now add the units:
8 + 9 + 5 + 1 = (8 + 5) + (9 + 1) = 13 + 10 = 23.
(If two numbers add up to ten, it's always convenient to add them up first.)
Well, now there are 82 tens, i.e. 820 plus 23 is 843.
Now let's move on to a more interesting topic - multiplication of two-digit numbers. Here we will also act unusually. The technique that we will now consider is called multiplication "cross" or Hindu way of multiplication.
We want to multiply 76 by 28. We proceed as follows:
First, we multiply the units: 6 8 = 48,
now we multiply with a “cross” 7 8 + 2 6 \u003d 56 + 12 \u003d 68 tens, and taking into account 4 tens out of 48, we have 72 tens and 8 units or 720 and 8. Now we multiply hundreds: 7 2 \u003d 14 hundreds or, taking into account 7 hundreds out of 720, we have 21 hundreds, 2 tens and 8 units. Answer: 2128.
We have considered a method that works for any two-digit numbers, but often the calculations can be simplified by noticing certain features of our multipliers.
For example, in our case, 76 is nothing more than 75 + 1.
Then: 28 76 = 28 (75 + 1) = 28 75 + 28 = 28 (50 + 25) + 28 = 28 50 + 28 25 + 28 = 2800/2 + 1400/2 + 28 =
1400 + 700 + 28 = 2128
Of course, we do not paint all these calculations, but we do them in our minds. They, like the drawing with a cross, are given in order to show the multiplication algorithm. In fact, all calculations are carried out "in the mind." Yes, at first, calculations using this method may seem complicated, but we do not forget about the second component of success - practice. A little practice and you'll be fine!
Well, for inquisitive "theorists" we will show how this method was invented.
Consider the multiplication of two two-digit numbers in general terms: multiply ab by cd.
We can always write ab as a 10 + b and cd as c 10 + d. Then:
(a 10 + b)(c 10 + d) =
100 a c + 10 a d + 10 b c + b d =
A c 100 + (a d + b c) 10 + b d
It can be seen from the multiplication result that in order to get hundreds, it is necessary to multiply the first digits of our number, to get tens - we multiply them with a cross and add them up, and finally, multiplying the last digits gives us the number of units.
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Objectives: secondary comprehension of already known knowledge, development of skills and abilities for their application.
Type of lesson: lesson - a fairy tale, consolidation of knowledge.
Lesson objectives:
1. Educational: repeat the learned method of adding and subtracting two-digit numbers, based on bitwise addition and subtraction.
2. Developing: to develop students' computational skills, creativity, development of logical thinking, attention, memory.
3. Educational: to cultivate interest and inquisitiveness in the process of learning, to cultivate mutual assistance, support, collectivism.
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MOU "Krasnoyarsk secondary comprehensive school No. 1"
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Primary school teacher
MOU "Krasnoyarsk secondary school No. 1"
Tanatova Gulmira Salauatovna
year 2009.
Mathematics Grade 2
Subject: Addition and subtraction of two-digit numbers.
Goals: secondary comprehension of already known knowledge, development of skills and abilities for their application.
Lesson type: lesson - a fairy tale, consolidation of knowledge.
Lesson objectives:
1. Educational: repeat the learned method of adding and subtracting two-digit numbers, based on bitwise addition and subtraction.
2. Developing: develop students' computational skills, creativity, development of logical thinking, attention, memory.
3. Nurturing:to cultivate interest and inquisitiveness in the process of learning, to cultivate mutual assistance, support, collectivism.
Equipment: caskets with numbers, drawings depicting a stone, the Serpent Gorynych, the evil sorceress Karchena, the textbook "Mathematics" Grade 2.
During the classes.
1. Organizing time.
Hello guys!
Today I will give you a lesson in mathematics, Gulmira Salavatovna.
Check if everything is ready for the lesson. Before we start our lesson, I want us to smile: you to me, and I to you; and you to each other and our guests. So, are you ready to start the lesson? Well, that's great.
You are a good friendly class.
Everything will work out for us.
2. Calligraphy.
U. Guys, do you like fairy tales?
Today at the lesson we will get into a fairy tale with you. Let's use the magic number. What is the most common number in fairy tales?
D. Number 3.
U. Where is it found?
D. Three wishes for a fish, thirty-three heroes, three inscriptions on a stone, three sisters, and so on.
U. Give me two-digit numbers in which there are 3 units and write down these numbers.
Sit right, write beautifully.
D. 13,53,73,83 etc.
U. From a series of numbers, tell me the smallest number and underline with one line, and name largest number underline with two lines.
Slide #1 (topic)
3. Message of the topic of the lesson.
U. Since our fairy tale is not simple, but mathematical, we will not only travel, but also repeat the method of adding and subtracting numbers, we will fight tricky tasks.
4. Oral account.
And now we will solve fairy-tale problems orally.
Slide #2
No. 1 Baba Yaga asked Ivan the Tsarevich 10 easy riddles, and 5 more difficult ones. How many difficult riddles did Baba Yaga ask Ivan Tsarevich? (fifteen)
Slide #3
No. 2 Squirrel gave the Hedgehog 18 large mushrooms, and small ones - 5 less. How many small mushrooms did the Squirrel give to the Hedgehog?
Slide #4
№3 Santa Claus has 8 teddy bears and 20 bunnies in his bag. How many fewer bears than bunnies are in Santa's bag?
What fairy tale characters did you meet?
Guys! And what fairytale heroes Do you know more?
Well done! And today we will meet with some heroes?
Slide #5
U. There was once a great strong kingdom in the world. Beautiful brave people lived in it. They were not afraid of anyone, but they themselves never quarreled with anyone. And all because Elena the Wise ruled them. The evil sorceress Karchena was very jealous of their happiness. So she decided to kill Elena. lured her in,
bewitched.
Slide #6
And she threw caskets to her faithful servants, and mysterious signs above them.
What are these signs? (these are numbers)
W. - What are these numbers?
D. Two-digit numbers.
U. We will have to work verbally with two-digit numbers and help open the right box. Read the numbers written above the lids
D. 35, 33, 73, 40, 13, 23.
U. What number is superfluous? Why?
E. The number 40, since there are only round tens in this number. All other numbers have tens and ones.
U. The box with the number 40 was opened, and there was a letter.
You won't find Elena, no matter how hard you try!
Can disenchant her magic flower,
And who I hid it from, you will understand if you go from large to small. Karchen.
Slide number 7
You need to try to arrange the numbers that are written above the caskets in descending order and write down the letters that are given with these numbers accordingly.
Write the numbers in a notebook in a line through the cell.
Landing.
On the board: 73, 35,33,23,13. (Student comes out)
Read the word you got.
Who has the magic flower hidden?
D. It turned out the word "Koschei", which means he has a flower.
U. The faithful servant of Elena the Wise Bulat, the hero on the road, gathered and went to get a flower. How long, how short, but the knight arrived at the fork of three roads, and there the stone lies and the inscription:
Who will read?
"You will pass three roads - you will find the way to Koshchei."
Bulat thought:
"On every road pass - time if you lose, and here every minute is precious, wisdom and beauty will be lost on earth without Elena.
5. Consolidation of the material covered.
U. Now all your knowledge, skills, what you learned in the last lessons will be useful to us. Let's check how well you can add and subtract two-digit numbers.
There are three roads in front of Bulat. There are three rows of desks in our class.
Let's help the knight go through all the roads at once.
Landing
The first row will go along the first road, collect all the pebbles, count the examples written on them.
Write the examples in a notebook in a line, and then check with each other. (One works at the blackboard., rate)
At the third row, the path is not easy - winding and steep. Look, make no mistake, do not fall into the abyss. (One at the blackboard works evaluation)
And we will follow the middle path with the second row, we will do our task.
Review the entry carefully.
Find the pattern by which the numbers are arranged in a row from the stone.
D. Numbers decrease, decrease by 3
U. Write down a series of numbers in full. (one at the board)
The children complete the tasks. – What did you get?
D. 20, 17, 14, 11, 8, 5.
U. Can we further reduce the series of numbers by 3?
D.Yes.
U. What number will turn out? (2) add.
And I'll see how the first and third rows are doing. Let's see if anyone stumbled on the path.
Records of students working at the blackboard are opened.
We check that all roads have passed.
Well done guys, they all did a great job.
And I suggest you take a break.
6. Physical Minute.
Slide #8
U. And here Koschey and his friend Zmey Gorynych meet us, hiss in unison with anger. Koschey says: “Since you were able to get to me, Bulat, you can also solve my problem.
Let's read the task.
On the desk: In my garden, an apple tree grows with golden and silver apples. Gold 25, and silver 12 less. How many apples are there?
Let's help Bulat solve this problem.
The decision is written at the blackboard with comments.
Z. - 25 yab.
WITH. - ? 25 less.
Total - ?
- 25-12=13 (yab) - silver
- 25+13=38 (yab) - total
Answer: 38 apples. Student assessment
Are there golden and silver apples in life?
What are the benefits of apples in real life?
Slide #9
We haven't solved all the problems yet. Three heads of the Serpent Gorynych prepared tasks for us.
Task number 1. Karchena has 28 bats in her service, and 8 fewer snakes. How many snakes does Karchena have?
Task number 2. On the way from Karchena to Koshchei, 9 of her faithful dwarf servants fled. How many dwarfs fled to Koshchei?
Task number 3. And the third head offers a task from the textbook: “Do the task - you will get a flower!” p.5 No. 5
7. Independent work. (additionally) slide 2
Problem 1. Baba Yaga asked Ivan Tsarevich 10 easy riddles, and 5 more difficult ones. How many difficult riddles did Baba Yaga ask Ivan Tsarevich?
Task 2. The squirrel gave the Hedgehog 18 large mushrooms, and small ones - 5 less. How many small mushrooms did the Squirrel give to the Hedgehog?
Task 3. Santa Claus has 8 teddy bears and 20 bunnies in his bag. How many fewer bears are there than bunnies in Santa's bag?
You won't find Elena, no matter how hard you try! A magic flower can disenchant her, and from whom I hid it, you will understand if you go from larger to smaller. Karchen. 23 33 73 40 13 35
23 33 73 13 35 35 - O 33 - Shch 73 - K 13 - Y 23 - E
Task. “In my garden, an apple tree grows with golden and silver apples. There are 25 gold apples, and 12 less silver apples. How many apples are there?
Task 1. There are 28 bats in the service of Karchena, and 8 less snakes. How many snakes does Karchena have? Task 2. On the way from Karchena to Koshchei, 9 of her faithful dwarf servants fled. How many dwarfs fled to Koshchei? Task 3. Textbook p. 5 No. 5.
Topic: "Subtraction of two-digit numbers with the transition through the discharge"
Type: lesson learning new material.
Technology: problem-based.
Lesson Objectives:
1. Introduce the method of subtracting two-digit numbers with the transition through the discharge; consolidate the studied computational techniques, the ability to independently analyze and solve complex problems.
2. Develop thinking, speech, cognitive interests, creative abilities.
3. To cultivate such qualities as kindness, mutual assistance, the ability to make friends and work in a group.
Equipment: Geometric figures, model examples, sample examples.
During the classes:
I. Organizational moment.
The lesson starts
He will go to the guys for the future,
Try to understand everything
Learn to unlock secrets
Give complete answers
To get a job
Only the mark "five"!
Hello guys! Hello dear guests! Today in the lesson we have to explore one very important topic. Do you agree? When scientists research something, they check everything that is related to the subject of their study. And before we find out what this topic is, we must consider it, but first I propose to solve several tasks.
The motto of the lesson: "Believe in yourself and everything will turn out!"
II. Updating of basic knowledge. Verbal counting.
1. Logical task.
- To prove that you are real explorers, you must solve a "tricky" problem.
Murka meows quieter than Barsik, but louder than Pushka.
Who meows the loudest?
(Barsik.)
2. Exercise to develop the ability to reason.
-Look at the pictures.
How can these figures be divided into parts?
(By color, by shape, by size.)
-Make an equation.
6 + 1 = 7 (by color)
5 + 2 = 7 (in form)
3 + 4 = 7 (by size)
3. "Mathematical relay race" Solving examples for subtraction with the transition through the category within 20.
One row participates, the rest of the students are judges. For the correct answer, the judges thank the student - they clap, for the mistake - there is no applause: (similar to column 2)
15 – 7 = 16 – 8 =
14 – 7 = 11 – 4 =
17 – 9 = 15 – 8 =
D. How can these examples be divided into groups?
D. By the value of the difference - 8 or 7.
E. For examples in which the subtrahend is equal to the difference and not equal to the difference.
E. Subtrahend is 8 and not 8
U. What do all examples have in common?
E. The same method of calculation is subtraction with the transition through a dozen.
U. What subtraction examples do you still know how to solve?
D. To subtract two-digit numbers.
4. Solving examples for subtracting two-digit numbers without crossing the digit.
Number entry. Calligraphy.
The number that we will write is hidden in these words: sister, cut.
Guess what number it is?
69 – 64, 74 – 54, 85 -44 , 36 – 34, 41 – 24.
For 2-3 examples, the algorithm for subtracting two-digit numbers is spoken aloud: 69 - 64. Out of 9 units. subtract 4 units, we get 5 units. From 6 dec. Subtract 6 dec. , we get 0 dec. Answer: 5.
5. Statement of the problem of the lesson.
When solving the last example, children have difficulty (possibly different answers). There is a problem situation:
41 – 24 =?
U. How does the last example differ from the previous ones?
U. The purpose of our lesson is to invent a subtraction technique that will help us solve such examples.
III. "Discovery by children new topic»
U. Make a model of the example on the desk and on the demonstration canvas:
U. How to subtract two-digit numbers?
D. Subtract tens from tens, and units from units.
D. Explain again why there is a difficulty here.
D. There are not enough units in the minuend.
U. Is the minuend less than the subtrahend?
D. No.
U.Where did the units hide?
D. In the top ten.
U. What should be done?
D. Replace 1 ten with 10 ones.
(Opening!)
U. Well done! Solve this example now.
Children replace in a reduced triangle-ten with a triangle on which 10 units are drawn.
11 units - 4 units. = 7 units, 3 dec. - 2des. =1 dec.
D. In total it turned out 1des. And 7 units, or 17.
U. So, Julia offered us a new calculation method. It consists in the following: split a dozen and take the missing units from it. Therefore, we could write our example and solve it like this (the record is commented on).
41 –
24
17
- And what do you think, what should always be remembered when using this technique? Where is the error possible?
E. The number of tens is reduced by 1.
IV Primary consolidation with pronunciation.
1. Comment on the first example according to the model.
D. 32 - 15. From 2 units. cannot subtract 5 units. Let's break ten. Out of 12 units subtract 5 units, and from the remaining 2 des. subtract 1 dec. We get 1 dec. 7 units, that is 17
VI Fizminutka.
- Read the numbers 56 and 98. What did you notice? Which number is greater? We work with a large number.
- Lean forward as many times as there are units in this number.
Children bend over 8 times.
- How many times did you bend over? (eight)
- Clap your hands as many times as there are tens in the number
- How many times did you clap? (nine)
- Jump as many times as there are units in the number 56.
-How many times did you jump? (6)
-Blink as many times as there are tens in 56. (5)
VII. - You convinced our guests that you are real researchers of everything new, and now we will consolidate everything that we remember using our algorithm.
Work with the textbook. page 177. Once again we pronounce the examples and write them down in a column. (The work is done collectively with commenting)
D. 67 - 59 = 8 I write units under units, tens - under tens. I subtract units: from 7 units. you can't subtract 9. I'll take 1 dec. 17 -9 \u003d 8 units. I write 8 under units.
I subtract tens: 5-5=0 Answer: the difference is 8
(similar to other examples)
VIII Independent work with a check in the class.
I suggest that the children choose from the expressions written on the board examples for a new computational technique.
- Choose from the expressions written on the board, examples for a new computational technique.
On the desk.
98 – 19 64-12 76-18
89-14 54-17
Children write down the necessary examples in a notebook in a cage, and then check the correctness of their notes according to the finished sample.
98- 76- 54-
19 18 17
After that, they independently solve the recorded examples. After 2-3 min. showing correct answers.
-Check if you have solved the examples correctly?
U. Find a pattern.
Children may notice that the numbers in the minuend are written in order from 9 to 4, the subtracted ones go in decreasing order.
-Write your own example that would continue this pattern, and solve it. (32-16=16)
IX Problem solution. page 177.
Charade.
The preposition is in my beginning,
At the end Vacation home.
And we decided everything
Both at the blackboard and at the table. (task)
Read the task.
What is known about the problem?
-What do you need to find in the problem?
- Can we immediately answer the question of the problem?
- How many steps does this task take?
The solution of the problem.
Comedy -27
Fiction -? 15 less
1) 27-15=12(f)
2) 27 +12=37 (f)
Answer: 37 films.
He's been my friend for a long time
Every corner is right.
All four sides
Equal length.
I'm glad to present it to you
What is his name? (square)
Task: Find the perimeter of a square if the length of its 1 side is 3cm
Given:
a=3cm
Find: R
Decision:
R \u003d a + a + a + a
R=3+3+3+3=12 cm
Answer: P = 12 cm
X. Lesson Summary
Let's sum it up now
Maybe the lesson was in vain?
U. What examples did you learn to solve? What did you learn new?
E. Subtraction of two-digit numbers with the transition through the discharge.
U. Can you now solve the examples that caused difficulties at the beginning of the lesson?
- Come up with an example for a new computational technique!
Homework
- The task today is creative.
-You need to make five examples for a new computational technique.
Solution of the problem p. 177 No. 2 (b)
Class: 2
Subject:"Addition and subtraction of two-digit numbers".
Goals:
- consolidate the ability to represent two-digit numbers as a sum of bit terms; repeat the relationship between the part and the whole; to consolidate the ability to solve word problems.
- teach how to add two-digit numbers with two-digit ones without going through the discharge;
- develop mindfulness, thinking; nurture a sense of mutual assistance and mutual assistance.
Equipment: graphic cards for indicating numbers, task charts, envelopes with tasks, Appendix 1 (computer presentation using fragments of the fairy tale "Geese Swans").
DURING THE CLASSES
1. Orgmoment
- Prepare for the lesson
The long-awaited call is given -
The lesson starts.
Here are examples and tasks
Games, jokes, everything for you!
I wish you good luck -
To work, have a good time!
2. Work on the material covered
On the desk:
4 22 10 20 18 6 12 2 24 8 16 26 14
- List the numbers in ascending order. Write them down in a notebook.
What did you notice as you rewrote these numbers? (Each next number is 2 more than the previous one).
What two groups can we divide this series into? (For double and single digit numbers)
What is the difference between a one digit number and a two digit number? (A one-digit number requires one character (digit), a two-digit number requires two)
What is the name of the first digit on the right of a two-digit number? (unit digit)
What is the name of the second digit from the right in a two-digit number? (tens place)
- Guys, what do you think, why do we need to know the ranks? (Unmistakably be able to solve any examples)
- Name the bit terms of numbers.
On the desk:
35 is 3 days and 5 units.
92…
56…
Textbook work
- Let's complete the task number 1 (c). Let's fill in the empty boxes. (Selectively invite to answer at the blackboard)
48 = 40 + … 70 + 3 = … 21 = 1 + …
96 = … + 6 5 + 80 = … 39 = … + …
3. Announcement of a new lesson topic and its tasks
– Today we will continue to work with two-digit numbers, learn how to add and subtract them correctly.
4. Working on new material(sample on the typesetting canvas)
- Let's see how the example is graphically written.
What do the triangles mean?... (tens)
What do the dots mean?... (Units)
- Let's read an example.
Reading from the spot: Twenty-four plus thirteen equals thirty-seven.
- Let's write it down using numbers: 24 + 13 = 37.
(Children express their opinion)
- To fold...
RULE-INCLUSION
- The following example is graphically written on the board.
- Let's read it.
…Forty-five minus fourteen equals thirty-one.
- Let's write it using the numbers 45 -14 \u003d 31
- Let's conclude: to subtract two-digit numbers, you need to subtract units from units, and tens from tens.
- Read on p. Rule 68...
5 .Physical education minute
We have worked together
A little tired
Fast all at once
They stood behind the desks.
We raise our hands, then we part.
Let's clap our hands, then shake them.
Look right, look left
And take a very deep breath!
(can be repeated)
–
During our vacation, the heroes of the fairy tale "Geese-swans" came running to us for help. This is Mashenka and her brother Ivanushka. The sister and brother ran to the milky river. They see: swan geese are flying. They asked the river
- River, mother, hide us!
River: If you succeed with my task, then I will cover you.
- Guys, we will help Masha and her brother, we will quickly complete task number 2.
The river covered them with a jelly bank. Geese-swans did not see, they flew by. The girl and her brother ran on, but the swan geese returned. What to do, who to ask for help ...
... They see an apple tree ...
Apple tree: If you guys can solve the examples on your own, then I will help you hide ...
1 option - 1 column
2 option - 2 column
1 option: Option 2:
36 +
42
69 – 21
44 –
13
72 + 24
52 +
15
85 – 43
Work in pairs
- The guys will check whether we completed the task correctly, rescued the children.
- They exchanged notebooks, checked with each other. (1st century checks 2nd century, and 2nd century checks 1st century)
The apple tree was covered with branches, covered with sheets ...
The geese flew past, and the girl and her brother ran on. We ran to the stove. They see the swan geese flying again...
Bake. The stove gave the most difficult task. Mashenka and her brother cannot do without our help.
Read the problems, choose the right scheme for them and choose the right solution. This is task number 4
- Read the 1st task. Let's choose the desired scheme. Let's find a solution, etc. of the 2nd and 3rd problems.
We helped the heroes of the fairy tale. The oven hid the children. Geese-swans flew, flew, shouted, shouted and flew away to Baba Yaga with nothing. Happy sister and brother ran home, where their father and mother and gifts were waiting for them.
- Good deeds and deeds are rewarded! For work in the lesson, for helping the heroes of a fairy tale, you also get “gifts”. Everyone has a gift in an envelope - this is the Tanagram game. The condition of the game will prompt task number 5 * "g"
7. Bottom line
What numbers did we work with in class? (With double digits)
How to add two digit numbers?
How to subtract two digit numbers?
It is a pity that the path is short,
It's time for us to return
But in the next lesson
Play again!
- Thanks to all! The lesson is over.
Math is hard
But I will say with respect -
Math needed
Everyone without exception!
12 d e to a bry.
To la ss naya p a bot.
11 – 8
15 – 8
Charging for the mind
70 ,
TOPIC OF THE LESSON:
ADDITION AND SUBTRACTION OF TWO-DIGITAL NUMBERS
need help
I doubt
I am confident and I can do it
Recall what is important for the lesson
50 – 7 = 80 + 5 =
43 – 21 = 34 + 45 =
60 – 4 = 76 – 6 =
We remember what is important for the lesson.
What do you know?
- Addition and subtraction table
- Add Action Component Names
- Names of Subtract Action Components
An algorithm for adding two-digit numbers, when the sum is a round number.
- Algorithm for subtracting from a round two-digit number
- Have you considered all the ways to solve expressions?
- Are there any problems, and what are they?
- Algorithm for solving expressions in a column for addition with a transition through a discharge.
- Algorithm for solving expressions in a column for subtraction with a transition through the category.
- Group work:
- 26+18=?
- 44-18=?
Stacking units...
14 ones is 1 ten and 4 ones
I write 4 under the units, and I write 1 ten over the tens
Adding dozens...
I add 1 ten, which was obtained from the addition of units
In total it worked out…
I write under tens ...
Reading...
I write tens under tens, and units under units.
subtract units. 4
I take one ten. (I put a dot over the number ...)
I'm counting 10 minus...
Under the units I write a number ...
Subtract tens. There were ... dozens. They took a dozen. Remained … tens. I count ... tens minus ... tens
I write under tens ...
Reading...
Examination
Choose and solve expressions for subtraction with transition through the category. What is the next expression?
Examination
I know
1. Addition and subtraction table.
I want to know
1. We have considered all cases of addition and subtraction.
found out
2. The name of the action components.
1. To find the value of the sum, you need to add the units, and if there are more than ten of them, then write down only the units, and remember the ten and add it when adding the tens.
3. Algorithm for adding two-digit numbers, when the sum is a round number
2. Are there any difficulties in solving expressions, and which ones.
2. To find the value of subtraction, you must first subtract units from units, but there are cases when the values of the units being reduced less value units subtrahend, it is necessary to take one ten. And when subtracting, strictly know that the number of tens has become one less.
3.Algorithm for adding two-digit numbers in a column with the transition through the discharge
4. Algorithm for subtracting from a round two-digit number
4. Algorithm for subtracting into a column with the transition through the discharge
3. Algorithm for addition in a column with a transition through a discharge
4. Algorithm for subtracting into a column with the transition through the discharge
