Question Video: Addition and Subtraction of Numbers up to 999 Then Rounding Mathematics • 3rd Grade

Video Transcript

Which number is nearest to 435 plus 169 take away 199? 400, 500, or 600.

The calculation in our problem contains three three-digit numbers and contains two different operations. 435 plus 169 take away 199. The question is asking us to find the number that’s nearest to this value. Finding a number that’s near to the answer to a calculation is a good way of estimating, of giving a rough answer of what we think the answer’s round about. There are lots of ways we could solve this problem. We could find the actual answer to the calculation and just see which of the three numbers it’s nearest to. But if we did that, we wouldn’t have done any estimation, and it wouldn’t be very quick.

So instead, we’ll practice our estimation skills. And the first thing we can do is to look at the final number in our calculation and to see what it’s close to. 199 is only one away from 200. So, let’s start by rounding that number up to 200. It is a lot easier to deal with. In a calculation like this, we need to work from left to right, so we need to add the first two numbers to begin with. We’re not gonna add the numbers as they are. Let’s just add the hundreds and the tens parts. 400 plus 100 equals 500, and 30 plus 60 equals 90. So altogether that’s 590. And if we take away 200 from 590, we get the answer 390. And 390 is nearest to 400.

Instead of working out the answer exactly, we rounded one of the numbers and only looked at the hundreds and the tens in the other numbers. This way we could find a quick estimate as to the answer. 435 plus 169 take away 199 is about 390. And out of our three numbers, the number that’s nearest to 390 is 400.