Rounding decimals to the hundredths on the number line
About this video
This video rounds decimals using a number line. Point A at 2.483 is closer to 2.48 than 2.49, so it rounds down to 2.48, and a number exactly halfway rounds up. In a second problem, points between 5.4 and 5.5 are compared with the halfway point 5.45 to find that only point C rounds to 5.5.
You'll be able to
- find the two hundredths or tenths a decimal lies between.
- use a number line to round a decimal to the nearest hundredth or tenth.
- use the halfway point to decide whether to round up or down.
Key words
- nearest hundredth
- The closest number with two decimal places, like 2.48 or 2.49.
- nearest tenth
- The closest number with one decimal place, like 5.4 or 5.5.
- halfway point
- The number exactly between two choices, like 5.45 between 5.4 and 5.5.
- round
- To replace a number with the closest simpler number at a chosen place value.
Transcript
- [Narrator] We are told point A is grafted 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. Alright, so let's just think about the candidates, which hundredths could we round to?
So if we're thinking about place value, so A right over here is 2.483. So this is the one's place, this is the tenths 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 wanna round up to increase our hundredths to 2.49 over there.
Now we don't wanna just round to any hundredth, we want to round to the nearest hundredth. And 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 half 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 tenths 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 do? 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 the 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.
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