Subtraction is easy if you're working on lesser (smaller) numbers. You've already learned how to subtract lesser numbers. You know that some two-digit problems require regrouping (borrowing).
But subtraction with regrouping is challenging when dealing with greater (larger) numbers. That's why you need to practice rewriting greater numbers for regrouping.
Say you need to subtract 391 from 675. You subtract in the ones place: 5 minus 1 equals 4. Now you subtract in the tens place. What is 7 minus 9? You can't take away 9 from 7. So you regroup a ten from the hundreds place. (You will sometimes see the terms "ones column", "tens column", and "hundreds column" used.)
To solve the problem, let's practice regrouping hundreds to tens. Remember that regrouping means taking from the place value to the left and adding it to the place value where you cannot subtract.
When you rewrite numbers for regrouping, you end up with a two-digit value in one of the place values. Look at this example again: 675 minus 391. In this problem, underline the 7. That means that you want the 7 changed into a two-digit value.
What's the digit you'll cross out? You cross out the 6 and write above it the number one less, which is 5. This shows that you take from the hundreds place and add it to the tens place.
Write the 1 you regrouped in the tens place.
What's the new two-digit value in the tens place? Correct-it's 17.
Now you can solve the problem 675 - 391.
The difference (answer) of 17 and 9 equals 8, and the difference of 5 and 3 equals 2. Write them in their proper place value under the equal bar.
See how it's easier to solve when you rewrite the numbers for regrouping?
