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## Arithmetic (all content)

### Course: Arithmetic (all content)>Unit 2

Lesson 9: Strategies for adding and subtracting within 100

# Adding by making a group of 10

Sal adds 5+68 by breaking the 5 into a 2 and a 3.

## Want to join the conversation?

• I'm doing a practice on "Add 2-digit numbers by making 10" and on this question says
"25 + 47 is the same as ___ + 50". And I used the hints and it said 3 ones from 25 to 47.
Where did the 3 ones come from?
•  The 3 ones come from the 25 and are added to the 47 to make 50.
So 25-3 = 22 and 47+3 = 50.
This makes the new sum 50+22 (or 50+22 as I would prefer) which is a sum that does not require carrying any 1's over (so its an easier sum).
• Hi, I am having some trouble with Adding by making a group of ten. Would anyone have a suggestion for me? I watched both videos, but I didn't get much out of them.
•  Look at the bigger number, how much do you need to add to it to make a ten number (10, 20, 30, 40....)
You can take that amount out of the other number and add it to the bigger number. Now you can add them together more easily because the bigger number is a ten.
For example: 7+26
How much do I need to add to 26 to make 30?
2 6+ 4 = 30 so I need to take 4 away from 7.
7 - 4
= 3
So 30+3=33. It's the same answer as 7+26, but for some people it's easier to make then 10 than add random numbers together.
• This is a bit difficult to swallow. It seems like it is just a way to complicate a relatively simple problem, but on the other hand it could help with larger numbers. The number line towards the end seems more helpful in remembering that the larger the number the further right one must travel on the line.

I think the answer would change depending on how you group the numbers in the parentheses too. Is that right?
• At what do those things mean (3+2)?
•  What those ( )'s are at are known as brackets or parentheses. These are used alot in more complex equations to seperate the different terms.
• Why can't you add 8+5 then 60+ the answer for 8+5 (which is 13) wouldn't it be easier?? I really don't get it could someone give me an opinion or answer??
• For some people it might be harder and for some people it might be easier. For example, I would split the five into 2 + 3 and add the 2 to 68 to get 70 and then add the 3 to get 73, but some people think that's harder. It really depends on what you think is easiest. So you can definitely do that if you want!
• but what happens if you get a question like 47 ➕ 23 now what?
• There are multiple methods for 2 digit (a number with two numbers in it) addition. E.g, the column method, a relatively easy one:

Think of it like this, you put the numbers into two columns:
1) 47
+23
___
___
The first step you do, is add the two numbers in the first column from the right side: 7 + 3, that equals to 10.
2) 47
+23
___
__*0*
But 10 is a two digit number, we don't have any space to fit both digits. So we put the first digit from the left in that column, 0, and then:
3) 47
+23
___
__*0*
1
We carry the 1, from the 10, under the next column. It will help us find the answer but it is not part of the answer.
4) We now do the second column:
47
+23
___
__*0*
1
We add 4 + 2 = 6, there just one digit, 6 BUT
Remember, we have a 1 underneath that column, so we add that 1 to 6, 1 + 6 = 7. We add all the numbers in that column, 1 is in that column.
5) 47
+23
____
7_0_
̷*1̷*
We can cross out the 1 because we have already used it. Therefore, 47 + 23 = 70.
Remember to check that you've added all the numbers in each column. (I can't bold the text for some reason D:)
Here's another example:
1) 56
+90
___
___

2) 56
+90
___
__6 (6 + 0 = 0)

3) 56
+90
___
14_6 _ (5 + 9 = 14, we put the whole number in, because we don't have other columns or any other numbers to add.

56 + 90 = 146

I hope you get the general grasp of this method :) - I'm not good at explaining, have a nice day!
• • 