How do you subtract using regrouping?

Answer 1

"Regrouping" is a more modern word for "borrowing".

When subtracting with decimals, if you are trying to subtract a larger digit from a smaller digit, you "regroup" the next digit to the left by taking one away from it and adding 10 to the number you are subtracting from.

Example

84

- 19

_____

You can't subtract 9 from 4, so you take one away from the next digit over (the 8) and add 10 to the 4.

14 - 9 is 5 in the ones digits

7 - 1 is 6 in the tens digits

Now if you are subtracting mixed numbers, the regrouping process is essentially the same, except that instead of always regrouping by tens, we regroup by the denominator size.

8 1/5

- 3 3/5

______

We can't subtract 3/5 from 1/5, so we regroup one unit from the 8 into 5 fifths.

7 6/5

-3 3/5

_______

4 3/5

It is very easy when you get some practice doing it.