Round Decimals
Lesson
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You can round numbers when you want to estimate an answer, or when you don't need as precise a measurement as the one you are given.

The first thing to know about rounding decimals is that it works exactly like rounding whole numbers. To round to the nearest tenth, you do the same thing you do to round to the nearest ten, except that you are working with a different digit in the number.

A number line can help you round decimals.

0.70 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.80

0.7

 

0.72 is between 0.7 and 0.8. It is closer to 0.7. Round down to 0.7.

0.75 is halfway between 0.7 and 0.8. Round up to 0.8.

0.78 is between 0.7 and 0.8. It is closer to 0.8. Round up to 0.8.

0.8

We always want to keep two things in mind when we round any number. The first is what we are rounding to. In the above example, we are rounding to tenths, so we should end up with one digit to the right of the decimal point, because that is the tenths place.

Round to the nearest tenth. 0.68 The number 6 is in the tenth place.
First: look to the digit to the right of the tenth place. 0.68

Since the number is greater than 5 round up.

Round up: add 1 to the digit you are rounding to. 0.7 So, 0.68 rounded to the nearest tenth is 0.7.

The second thing to keep in mind is the method we are using to round by. In the nearest method we look at the digit to the immediate right of the digit we will round to. For this example we will look at the hundredth digit and if it is a five or greater (5 through 9) we round up (add 1 to the digit we are rounding and drop all the digit to the right). If the digit to the right of our rounding digit is less than 5 (0 though 4) we round down (drop all digits to the right of the digit we are rounding).

Example
number to be rounded to nearest tenth  341.75
number to the right of the tenths digit 5
since the number is a 5 we round up 341.8
So, the answer is 341.8
What if the number we were rounding was 341.747 instead?  
number to be rounded to nearest tenth 341.747
number to the right of the tenths digit 4
since the number is less than 5 we round down. 341.7
So, the answer is 341.7  

 

Remember: If less than 5, round down. If 5 or greater, round up.

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