In this video, we're going to look at how to round numbers, like these ones, to a certain number of decimal places. Let's start with this question, and round 8.3175 to two decimal places. Because we're being asked to round to two decimal places, we start by identifying the digit that's two places from the decimal point, which in this case is the one. We call this one the last digit, because it's the last digit that we want to have in our answer. The digit to the immediate right of this, so the 7, is called the decider, because this is the one that we look at to decide whether we need to round up or round down.
If the decider is 4 or less, so 0, 1, 2, 3 or 4, then we leave the last digit as it is. but if it's five or higher, so five, six, seven, eight or nine, then we round up the last digit. So as our decider is seven, we have to round our last digit up and change the one to a two. And then to finish, we just remove all of these other digits that come after the last digit.
So we rounded 8.3175 to 8.32. In this next one, we're being asked to round 217.631 to one decimal place. So because we're rounding to one decimal place, our last digit will be this 6, because that's one place to the right of the decimal points. And so the 3 will be the decider. Because 3 is in the 4 or less group, it tells us that we're going to have to round down.
And remember, when we round down, we keep the last digit as it is. So the 6 stays as a 6. This means that all we have to do is rewrite it as 217.6. And that's it. So effectively, we just got rid of the 3 and the 1. In this last question, We're rounding 17.3695 to three decimal places. So this time the 9 would be our last digit, because it's three places to the right of the decimal point, and the decider would be the 5, because that's the next digit to the right.
Because the decider is a 5, it means we're gonna have to round our last digit up. But when you have to round up a 9, it's kind of tricky. because the 9 gets rounded up to a 10, which means that the 1 is in the column to the left, and so we have to add it to the 6. So in this case, our 6 becomes a 7, and we bring down the 0 as well, so that overall we end up with 17.370. Another way of thinking about it that you might find easier is to think of it as if we're rounding this 69 up to 70. The last thing to point out is that we have to keep this zero in our answer, because remember, we were asked to round to three decimal places. So if you just wrote 17.37 instead, then you wouldn't get all the marks, because that answer only has two decimal places.
Anyway, that's everything for this video. So I hope that made sense. If it was useful, then please do like and subscribe, and hopefully we'll see you again soon.