Rounding decimals to the hundredths on the number line | Grade 5 (TX TEKS) | Khan Academy

We are told point A is graphed on the number line below. We see that right over there. What is A rounded to the nearest hundredth? Pause this video and see if you can figure that out before we do it together.

All right, so let's just think about the candidates. Which hundredths could we round to? So if we're thinking about place value, A right over here is 2.483. So this is the one's place, this is the tenth place, this is the hundredth place right over here.

So we could round down to 2.48, which is right over here, or we might want to round up to increase our hundredths to 2.49 over there. Now we don't want to just round to any hundredth; we want to round to the nearest hundredth.

So my question to you is: which hundredth is A closer to? Is it closer to 2.48 or is it closer to 2.49? Well, it's pretty clear that it's closer to 2.48. So this is the nearest hundredth; this is what we would round to. We would round down to 2.48.

Now, some of you might be wondering: what if you were exactly in between those two hundredths? What if you were right over here? Well, the rule that mathematicians have come up with is if you're exactly halfway between those two points, you should round up. But that's not the scenario that we saw in this question, so A is clearly closer to 2.48.

Let's do another example. So here they say three points are graphed on the number line: points A, B, and C. If rounding to the nearest tenth, which point rounds to 5.5? So pause the video again and see if you can figure that out.

All right, so let's just think about the tenths that these dots or these points are between. At the high end, we have 5.5. Remember, if I have a number like 5.5 something something something, this right over here is the tenth place.

So all of these are between 5.5 and 5.4, so they're going to either round down to 5.4 or they're going to round up to 5.5. Well, let's just use the same reasoning we just used. Point C, where does that round to? Well, it's much closer to 5.5 than 5.4. You can just see that by looking at it, so C is going to round to 5.5.

What about Point B? Well, Point B, when you just eyeball it, it's a little bit hard to tell until you realize that this is the halfway point: 5.45 is a halfway point. Point B is not quite there, so this will round down to 5.40, and Point A is clearly even closer to 5.40, so it will round down as well.

So if rounding to the nearest tenth, which point rounds to 5.5? Well, we see that is Point C.