In this lesson, we're going to look at different ways that we can round whole numbers. Let's say, for example, that we want to figure out how many marbles are in this jar. If we want to figure out exactly how many there are, we can empty out the jar and count each marble one by one. And maybe we come up with 273. We could say there's exactly 273 marbles in the jar. But what if we're asked about how many marbles are in the jar? Whenever we see the word about, that's a clue that we're not interested in finding the exact number. We really just want an estimate. We can use a number line as one way of helping us to estimate how many marbles are in the chart. Now, notice that this number line here is broken down by hundreds. It's counting by intervals of 100 - 100, 200, 300, 400. Now, our 273, which we know is exactly how many marbles in the jar, we can see it falls pretty close to the 300. That's the closest 100 that 273 falls near. So we could say that there are about 300 marbles in the jar, and we could give that as our estimate. Now, what if our number line was broken down by tens instead of hundreds? This time, when we place our number 273 on the number line, we can see that the tens that it's closest to is 270. So if we want to round our number to the nearest tens place, it would be 270. So we could also say there are about 270 marbles in the jar. So our estimate of the number of marbles in the jar will depend on what place value we want to round to, whether we run around to the hundreds or to the tens place. Next, we're going to see how we can round numbers without having to depend on the number line. So let's go back to our number 273 and round it to the hundreds place. Our first step is to find the digit that's in the hundreds place, which in this case is the two. Next, we want to look to the digit that's to the right of that number. I like to call it the neighbor. The neighbor is going to help us figure out what we need to do with that two that's in our place value that we're focusing on. The two is either going to stay the same or it's going to go up by one and become a three. If the neighbor is less than five, then our place value number would stay the same. If the neighbor is five or more, then our place value will go up by one. And since seven falls into that second category of being five or more, then our place value digit is going to go up by one and the two will become a three. And then any digits after that automatically become zeros. So our number rounded to the hundreds place becomes 300. Now, if we want to round that same number to the tens place, we follow the same strategy. Except this time we're starting by focusing on the digit in the tens place, which is the seven. Next we look at the neighbor, which is the three. The neighbor tells us what our digit in the place value is going to do. Same rule as before, if the neighbor is less than five, our place value stays the same. If the neighbor’s five or more, our place value goes up by one. Since our neighbor, the three, is less than five, that tells us that our place value number, the seven, is going to stay the same. Any number that's to the left of our place value will also stay the same. So the two in front doesn't get affected by anything at all that would always stay the same no matter what's going on with the seven. So start off by keeping the two the same. Now we know that the seven is going to stay the same because the neighbor, the three, said that it didn't have to change. And now anything after it becomes zero. So the three becomes zero. So now our number rounded to the tens place is 270. When it was rounded to the hundreds place, it was 300. Rounded to the tens place is 270. But both numbers are valid estimates. It just depends on what digit we want to round it to. So to review, rounding gives us an estimated answer when we don't need to find an exact answer. In word problems, there are two particular keywords that let us know that we can give an estimate instead of an exact answer. The words about and approximately. So keep your eyes open for those words whenever you see those in a math problem, that lets you know that you don't need an exact answer and you can just round your answer. And that saves you time oftentimes as well. So the estimate depends on what place value we round to and it also depends on the neighbor. If the neighbor is less than five, our place value stays the same. And if the neighbor is five or more, our place value will go up by one. So now you know how to round whole numbers. Next we're going to take a look at how to round decimals.