Question Video: Finding the Difference between Three-Digit Numbers and Two-Digit Numbers by First Subtracting Tens Mathematics

Find the difference by first subtracting tens. 754 − 20 = _


Video Transcript

Find the difference by first subtracting tens. 754 take away 20 equals what.

In this question, we need to find the difference between two numbers or, in other words, subtract them. Now we’re starting here with a three-digit number, 754. And we’re being asked to take away 20. Now we know that 20 is a multiple of 10. It’s actually the same as two 10s. And the question gives us a hint as to find the answer. We’re told to first subtract the tens. In other words, we can take our number 754 and all we really need to look at, because there are five 10s in 754, is the tens part. Now we can see we’ve got a part–whole model to complete here.

Now as we’ve said already, the number 754 has five 10s. So we can take those five 10s, which are worth 50, and we can separate them out. And we’re left with the seven 100s and the four ones, 704. And we’ll put that to one side. We’ll come back to it at the end. But to start with, all we need to think about are our five 10s. Now we know that five take away two equals three. And so five 10s take away two 10s is going to leave us with three 10s. Let’s draw a part–whole model to show our answer. As we’ve just said, five 10s take away two 10s is going to leave us with three 10s. 50 take away 20 equals 30.

And then we’ve still got our 704 that we haven’t touched yet. And by looking at our two parts, we can see that our answer is going to have seven 100s, four ones, and of course the three 10s that we made when we subtracted. Because we’re taking away a multiple of 10 here, we’ve found the answer by concentrating on the tens. 754 subtract 20 leaves us with 734.

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