Decimal Places
When we work with decimals, we often need to approximate a number.
Suppose we did a calculation and the answer came out as
10.9315.
This number currently has 4 figures after the decimal point and we say that it has 4 decimal places.
We can approximate this number by using some rules:
If we wanted to give just 2 decimal places then we need to look at the 3 rd decimal place. If it is a 0, 1, 2, 3 or 4 we replace it and any following figures with a zero – we say it has rounded down. However if it is a 5, 6,
7, 8 or 9 then we not only replace it and any following figures with a zero but we add 1 to the preceding digit – we say it has rounded up.
So in our example
10.9315 becomes 10.9300 correct to 2 decimal places
In practice we do not bother with the final zeros and give the answer as
10.93 correct to 2 d.p. (d.p. is short for decimal places)
Sometimes we have to leave the zero in place though!
Suppose we need 0.897 correct to 2 d.p.
Then the answer is 0.90
As we were asked to give it to 2 d.p., we do need to give the second decimal place, even though 0.9 has the same value!
We can have any number of decimal places.
10.9315 is 10.932 correct to 3 dp
is 10.93 correct to 2 dp
is 10.9 correct to 1 dp
is 11 correct to 0 dp
So, the rules allow us to decide which is the closest approximation to the accurate answer.

Example
The number 3.141592653589793238462643383279… is a famous number in Maths called pi.
(a) Round pi to 2 d.p.
The 3 rd d.p. is 1, so we round down. The answer is 3.14.
(b) Round pi to 3 d.p.
The 4 th d.p. is 5, so we round up, this turns the 1 into a 2. The answer is
3.142.
(c) Round pi to 12 d.p.
The 13 th d.p. is 7, so we round up, this turns the 9 into a 10, and we carry over. The answer is 3.141592653590
Note: We follow the same rules to round to the nearest ten or hundred, but make sure you keep the zeros needed to maintain the place value.
Example
Round 5379.03 to the nearest 100.
There is a 7 in the 10s column, so round the 3 up to 4. The answer is
5400
Remember you need the zeros up to the decimal point, as 54 would not be a very good approximation of 5379.03