The distance between two cities is 28655 metres. Round this distance to the nearest kilometre.
In this problem, we are given a distance in metres. And we’re asked to round this distance to the nearest kilometre. There are two methods we could use to find the answer. And both methods involve us applying what we already know about kilometres and metres and converting between the two. Let’s start my reminder ourselves the number of metres in a kilometre. One kilometre is the same as 1000 metres. This means that every whole kilometre is a multiple of 1000 metres. One kilometre is 1000 metres, two kilometres is 2000 metres, and so on.
In our first method, we can think about the number 28655. Which two multiples of 1000 is this number in between. Well, it comes in between 28000 and 29000. This is equal to 28 kilometres and 29 kilometres. But where on the number line does our number belong? When we’re rounding like this it’s always useful to mark a halfway point. This is worth 28500. So we can estimate that 28655 might be around here on the number line. It’s certainly to the right of 28500. And so the nearest multiple of 1000 to this number is 29000. We round the number up. And as we’ve said already 29000 metres is the same as 29 kilometres. And so we’ve worked out that 28655 metres rounded to the nearest kilometre is 29 kilometres.
A second strategy we can use is to take our measurement which is in metres and to convert it before we start into kilometres. As we’ve said already, one kilometre is the same as 1000 metres. So to change metres into kilometres, we need to divide by this number, divide by 1000. When we divide a number by 1000, the digits in that number move three places to the right. So let’s see what happens to 28655 as we divide it by 1000. First, we’ll shift it one place. Now, we’ll shift it a second place and, finally, a third place. We seem to have swapped a comma for a decimal point. 28655 metres is the same as 28.655 kilometres.
Now that we’ve found the distance in kilometres, we just need to round this distance to the nearest whole kilometre. 28.655 is somewhere in between 28 and 29. Let’s find a halfway point again to help us. Halfway between 28 and 29 is 28.5 or 28 and a half. So once again, we can see that 28.655 is to the right of this number, perhaps about here on the number line. And so as we saw before, the nearest whole kilometre is 29 kilometres, two different methods but they both give the same answer. If we have a distance in metres, 28655 metres, and we need to round it to the nearest kilometre, the answer will be 29 kilometres.