Rounding is a process by which you can write a long number as a shorter number with roughly the same value. The tenths digit is the digit immediately to the right of the decimal point, such as 5 in 12.578. When you round a number to the nearest tenth, you shorten it so that only the tenths digit appears right of the decimal.

To round a number to the nearest tenth, it must have numbers in both the tenths and the hundredths digits. For example, you can round 3.7891, 1.552 and 18.12 to the tenths digit, but you can't round the whole number 8 or the number 17.5 to the nearest tenths.

Determine if the hundredths digit  the number two places to the right of the decimal point  is 4 or below  or if it's 5 or above.

If the hundredths digit is five or above, add one to the tenths digit. This is called rounding up. Write out the number with the new tenths digit. Do not include any of the numbers to the right of the tenths digit.
For example, in 3.7891, the hundredths digit is 8. So, this means that in the tenths digit, you add 1 to 7, to result in 8 in the tenths digit. And now you write the number again to the tenths digit: 3.8.
If the number you are looking at is in the hundredths digit, you still round up. So, 1.552 rounds to 1.6.

If the hundredths digit is 4 or below, then you don't change the tenths digit. Rewrite the number with all digits to the right of the tenths digit removed. This is called rounding down.
For instance, in the number 18.12, the hundredths digit is 2. So you round down and rewrite the number as 18.1.
If the hundredths digit is 0, you also round down. So, 201.809 rounds to 201.8.
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