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

Lesson 11: Subtraction within 100

# Subtracting 2-digit numbers without regrouping 1

Sal subtracts 23 from 65 by thinking about tens and ones.

## Want to join the conversation?

• What is a column?
• a column is just a vertical area, so all the elements in the column are stacked on top of each other.
you can see in the video that the ones "column" is just the vertical area that he dotted around and all the elements inside that column (the 5 ones, the 3 ones and the 2 ones) are put each one on top of the other.
• When you "carry" digits what is that referring to
• Hi Lynel. A carry is a digit that is transferred from one column of digits to another column of more significant digits. For ex. when 6 and 7 are added to make 13, the "3" is written to the same column and the "1" is carried to the left.
• Is there a reason why the numbers are stacked on top of each other for problems like this? Like, why do you put the 65 above the 23?
• Well, one: to line up the places so no mistakes would be made. And two: to make it easier for regrouping. My 4th grade teacher called this old-fashioned math and I guessed I kinda liked it. But 65 and 23, I just do it in my head because they're pretty simple equations. But if I was working with decimal places or multiplication or addition with four 3-digit numbers, I would stack them up.
• I have a question. When you have a zero, and you need to borrow from it, you cross it off, and put a nine, right? But, what if you need to subtract zero from another number that is higher than zero, like 5? Do you cross off the nine and put an eight? :o
• No, you do not put a nine. You put a ten. Then you subtract the numbers.
Your second question is asking what is 5 minus 0. In this case, since zero is at the bottom, you can take away nothing from five. The answer is five. But if it is 0 minus 5, you will be going in the negative side of the number line. This would mean that 0 minus 5 is -5. Draw the number line. Start at zero. Minus means to the left. Plus means to the right.

If you have a five in the ones place and a nine on the bottom (i.e. 765 minus 39), then the five becomes into a 15 and the 6 becomes into a 5.
Think about it like this: if you are decreasing the 6, you are removing ten from the number, which is going to change the problem, which you do not want. So, to compensate for that "lost" ten, you add it to the five, and make it into a fifteen, so you can remove 9, since you cannot remove 9 from 5 (in this case since the first number in its entirety is larger than the second number).
Hope this helps:)