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.
