Video: Simple Subtracting: Subtracting One-Digit Numbers from Three-Digit Numbers

Find the difference by first subtracting ones. 629 − 7 = _

02:55

Video Transcript

Find the difference by first subtracting ones. 629 take away seven equals what?

In this problem, we’re asked to find the difference between two numbers. We know that to find a difference, we need to take away the smaller number from the larger. So, the calculation is 629 take away seven. What does 629 look like? Six 100s, two 10s and nine ones, 629. Now, we’re asked to take away seven. Seven is a number of ones. It doesn’t have any hundreds or any tens in it.

Now, we know the number that we’re starting with has nine ones. So, the first thing we can do is to partition the number so that those nine ones are separate. In fact, the question tells us to find the difference by first subtracting ones. So, let’s shift our nine ones to one side. Here we go. We have one part on the left, 620, and on the right we have the important nine ones that we need to subtract from. So, we need to begin our subtraction just by concentrating on the nine ones. And, we need to subtract seven ones. Watch how the number of ones changes as we subtract seven ones. One, two, three, four, five, six, and seven. We started with nine ones, we took away seven ones, and now we’re left with two ones. Nine take away two equals seven.

Let’s look at the two parts of our number now, and we’ll combine them back together again. On the left, we have six 100s and two 10s. We know this is 620. This number hasn’t changed. Although we had nine ones to start with, we’ve taken away seven ones. So on the right-hand side, the part shows two ones. We can combine our two parts together to make the answer. Our answer contains six 100s, two 10s, and two ones. We found the difference by first subtracting the ones. 629 take away seven equals 622.

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