Do you know what to do when you are trying to do a subtraction question and one of the numbers in the bottom line is bigger than the number above it? When the digit you’re taking away is bigger than the digit you’re trying to take it away from, you need to know a method to solve the problem. In this lesson, you will learn how to trade between place value columns to solve this problem. Let’s try some subtractions where this problem occurs.
Look at this example, 54 take away 26. Fifty four is a bigger number than twenty 20 therefore that’s okay. Look at the ones column. The first thing we have to do is take six away from four. How can we do that? We’ll use place value columns to help us as well as unit squares and ten strips for the number so you can understand what’s happening. Let’s put the bigger number in the place value columns. Look at the ones column of the number sentence. We need to take six away from four. Look at the ones column of the place value column. We don’t have six ones to take away. We only have four. What we do is take one group of ten from the tens column, change it back to ten ones and put the ten ones in the ones column. This gives us fourteen ones in the ones column and only four groups of ten in the tens column. We can’t just steal those ten ones. We have to trade them from one column to the other or the sum will not turn out right. That’s all very well but we can’t always have ten strips and unit squares to help us work the sum out. How do we show what we have done in a normal sum? Looking at our sum, we changed the four in the ones column to 14 by placing a one just beside the four. We took ten out of the tens column so we need to change the five tens to four tens. Now we have four ten units in the ones column and we can take six away from that and that leaves eight. Put the eight in the ones column of our sum. Looking at the tens column in our sum, we have four take away two. Take away two ten strips from our four ten strips and that leaves two tens. Put the two tens in the tens column so the answer to 54 take away 26 equals 28.
