How to Round Off to the Nearest Number Using a Number Line
If you're teaching numbers to third graders, it's important to help them learn how to round numbers so they can understand this concept before moving on to using numbers for adding and subtracting. Because children still have trouble holding numbers in their mind, it's easier to explain how to round off to the nearest number using a simple visual such as a number line.
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Instructions
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Determine number place value needs to be rounded. Without this information, you would not know what number to round to. Take the number 653, for example. Each digit represents a different place value. The left digit is the hundreds place, telling you how many sets of one hundred there are in this number, which is 6 hundreds. The middle digit is the tens place, telling you how many sets of tens there are in this number in addition to the 6 hundreds, which is 5 tens. The right digit is the ones place, telling you how many sets of ones there are in addition to the 6 hundreds and the 5 tens, which is 3 ones.
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Draw out a number line. This is basically a straight line from with identically spaced line segments. So if you were rounding numbers such as 12 and 66 to the nearest number, you would draw a number line using multiples of tens such as 0, 10, 20, 30, 40, 50, 60, 70, 80 so that both these numbers, 12 and 66, can fit. This provides a clear visual in front of you to look at and it will make it easier to round.
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Place the numbers inside the number line. So, if you were using the numbers 12 or 66, you would place 12 between 10 and 20, but closer to the 10, and you would place 66 between 60 and 70, but closer to the 70. This will give you an idea of how to round to the nearest tens place using a number line.
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Use the general rules of rounding. Usually you round down or round up, but since you're using a number line, you will round to the left or right. For example, if the ones digit is 0, 1, 2, 3, 4, then using a number line, you're going to round to the nearest number that's on the left. If the ones digit is 5, 6, 7, 8, 9, then using a number line, you're going to round to the nearest number that's on the right. So if you were using the number 12, the ones digit is 2, so you would round this number to the nearest tens number, which is 10. If you were using the number 66, the ones digit is 6, so you would round this number to the nearest tens number, which is 70.
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References
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