1. SIGNIFICANT FIGURES AND DECIMAL PLACES

2. Decimal places
It is often useful to give an answer to a number of decimal places.
If you are asked to round a number to 2 decimal places you must have
exactly 2 digits after the decimal point.
The following rules are used:
Count along the digits to the required number of decimal places.
Look at the next digit
If it is less than 5, leave the digit before it as it is.
If it is 5 or more, you must round up the digit before it.

3. 5.3472 Examples 1 Write 5.3472 correct to 2 decimal places.
the next digit is 7 so you must round up
= 5.35 to 2 d.p.

4. 36.4319 Examples 2 Write 36.4319 correct to 2 decimal places.
the next digit is 1 so the digit
before it will not change
= to 2 d.p.

5. 0.0088 Examples 3 Write 0.0088 correct to 2 decimal places.
the next digit is 8 so you must round up
= 0.01 to 2 d.p.

6. 126.2043 Examples 4 Write 126.2043 correct to 2 decimal places.
the next digit is 4 so the digit
before it will not change
= to 2 d.p.
note: you must keep the 0 in your answer

7. 27.998 Examples 5 Write 27.998 correct to 2 decimal places.
the next digit is 8 so you must round up
= to 2 d.p.

8. 49.3254 Examples 6 Write 49.3254 correct to 3 decimal places.
the next digit is 4 so the digit
before it will not change
= to 3 d.p.

9. 7.8798 Examples 7 Write 7.8798 correct to 3 decimal places.
the next digit is 8 so you must round up
= to 3 d.p.

10. Significant figures
You may also be asked to round to a number of significant figures.
To round a number to a given number of significant figures use the
following rules:
Count along the digits to the required number of significant figures.
(The most significant figure is the first non-zero figure.)
2. Look at the next digit
If it is less than 5, leave the digit before it as it is.
If it is 5 or more, you must round up the digit before it.

11. 53872 Examples 1 Write 53872 correct to 2 significant figures.
the next digit is 8 so you must round up
53872 = to 2 s.f.

12. 76408 Examples 2 Write 76408 correct to 1 significant figure.
the next digit is 6 so the digit
before it will not change
76408 = to 1 s.f.

13. 6.439 Examples 3 Write 6.439 correct to 3 significant figures.
the next digit is 9 so you must round up
6.439 = 6.44 to 3 s.f.

14. 0.00342 Examples 4 Write 0.00342 correct to 2 significant figures.
the next digit is 2 so the digit
before it will not change
= to 2 s.f.

15. 0.00899 Examples 5 Write 0.00899 correct to 2 significant figures.
the next digit is 9 so you must round up
= to 2 s.f.

16. Estimating
It is important that you know how to check if your answer to a calculation
is a sensible answer.
To estimate the answer to a calculation use the
following steps:
Round each of the numbers to 1 significant figure.
2. Do the calculation using your rounded numbers.

17. Examples
1 Estimate the answer to
2 Estimate the answer to

18. Examples
3 Estimate the answer to

19. Examples
4 Estimate the answer to 10 20