Question Video: Identifying the Correct Rounding of Three-Digit Numbers to the Nearest Ten Mathematics • 3rd Grade

The teacher asked Michael and David to round the number 572 to the nearest ten. Michael said, “The answer is 570.” David said, “The answer is 580.” Who is correct?

03:06

Video Transcript

The teacher asked Michael and David to round the number 572 to the nearest 10. Michael said, “The answer is 570.” David said, “The answer is 580.” Who is correct?

What’s happening in this question is the sort of thing that might happen in your maths lessons. A teacher has asked a question, but we’re getting two different answers from two different people. Who is correct? Now the task that both Michael and David have tried to do in this question is to around the number 572 to the nearest 10. And we’re given two possible answers. Either Michael’s right when he said the answer is 570 or David’s right when he said 580. One way we could find the answer is to look at the place value of the number that we’re rounding. Now we know that the number 572 is made up of five hundreds, seven tens, and two ones.

Now the first thing we can do with the digits of this number is look at that tens digit. This gives us an idea of the two multiples of 10 that this number lives in between. We can take this digit as it is but change the ones digit for a zero. This gives us the multiple of 10 that is less than our number, 570. And then we can add one to this digit to make it eight tens. And this would give us the multiple of 10 that’s larger than our number, 580. Our number is in between 570 and 580. And you can see that this is where Michael and David have both got their answers from. Michael has thought to himself, I need to round this number down. And David has rounded the number up. And to find out who’s correct, we need to look at another of the digits in our number.

This is the ones digit. Now there’s a rule for ones digits and rounding to the nearest 10. Do you remember what it is? If the ones digit is four or less — so that’s four, three, two, or one — we round down. And if the number ends in a five or more — so that’s five, six, seven, eight, or nine — we round up. Now that we’ve remembered this rule, we can apply it to this number. The number of ones in 572 is two. And this is definitely four or less, isn’t it? So we need to round down. 572 rounded to the nearest 10 must be 570. We’ve used place value and our knowledge of rounding to round 572 to the nearest 10. The answer is 570. So the person who is correct is Michael.

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