Sometimes, we have to rewrite the top number in a subtraction problem so we can solve the problem. In other problems, we can simply subtract. How do we know which problems can be subtracted quickly and which need to be rewritten?
Let's subtract 95 minus 42. First, we'll read the problem in the ones place (ones column).
The top digit in the ones place is a greater (larger) number than the bottom digit, so we can subtract. We don't need to borrow.
But what if we subtract 95 minus 48? The bottom digit in the ones place is a greater number.
Then we have to regroup (borrow) the tens and ones in the top number.
First, regroup one ten from the tens place (tens column) and add it to the digit in the ones place. Let's cross out 9 and replace it with a digit that is one less, which gives us 8.
Next, add a small 1 in front of 5 to show that it regrouped a ten from the tens place.
Now 15 is the top number in the ones place. Is it greater than the bottom number? Can we solve it? Let's first solve the ones place.
Then subtract the tens place. Remember, our new top digit is 8.
By using regrouping, the difference (answer) equals 47.
Remember: when the top digit is less than the bottom digit in the ones place, regroup the ones and tens digits. Only then can we solve the subtraction problem.
