Rounding is a process by which you can write a long number as a shorter number with roughly the same value. The tenths decimal place is the digit immediately to the right of the decimal point, such as the 5 in 12.578, so to round it out you need to look at the number to its right, which is the hundredths decimal place.
Precision of Decimals
To round a number to the nearest tenth decimal, the number you start with must be as precise as the 100 decimal place, which is the third number after the decimal point. For example, you can't round 8 to a tenth decimal place, or 7.5, but you can round out 8.12 and 7.59.
If the hundredths digit is five or above, add one to the tenths decimal place and delete the hundredths decimal place. 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, giving you 3.8. In the same way:
- 1.57 becomes 1.6
- 1.292912 becomes 1.3
- 1.560 becomes 1.5
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. Similarly:
- 2.01 becomes 2.0
- 1.92 becomes 1.9
- 1.52001 becomes 1.5
Working With Rounded Numbers
Once you round a number up or down, it loses the precision it once had so if you do additional calculations with it, the resulting number can only be as precise as the tenth decimal place. In most cases you should round out the resulting number to the tenth decimal place as well.