Many calculations result in answers that are more accurate than you need. In such cases the answers are rounded to the required degree of accuracy.
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In many calculations you will be expected to round off your answer to a given number of decimal places.
Round \(3.168\) to two decimal places.
\(3.168\) is correct to three decimal places as there are three digits after the decimal point.
If the number at the next decimal place is five or more add 1 to the previous decimal place.
With \(3.168\) the number at the third decimal place is five or more.
So, \(3.168\) rounds up to \(3.17\) (to two decimal places).
Now try the example questions.
Round \(17.839\) to one decimal place.
If the number at the next decimal place is smaller than five then leave the previous decimal place as it is.
With \(17.839\), the number at the second decimal place is smaller than five.
So, \(17.839\) rounds down to \(17.8\) (to one decimal place).
Express \(\frac{9}{{13}}\) as a decimal correct to 3 decimal places.
\(\frac{9}{{13}} = 9 \div 13 = 0.6923076\)
With \(0.6923076\), the number at the fourth decimal place is smaller than five.
So, \(0.6923076\) rounds down to \(0.692\) (to 3 decimal places).
Find \(\sqrt {8.9}\) as a decimal correct to 1 decimal place.
\(\sqrt {8.9} = 2.9832868\)
With \(2.9832868\), the number at the second decimal place is greater than five.
So, \(2.9832868\) rounds up to \(3.0\) (to 1 decimal place).