Decimals
SIGNIFICANT FIGURES
Significant means the most important numbers.
These are usually the largest ones.
To find significant figures we use the same skills as when we round
off decimals
Significant figures can be decimal numbers or whole numbers.
2.5
1.38
correct to 2 significant figures is
correct to 1 significant figure is
to 3 sig. figs is
to 2 sig. figs is
to 1 sig. fig is
2.5
3
1.38
1.4
1
Each time you are rounding off, leave the number of figures it asks
for. The numbers can be decimals or whole numbers.
0’s are counted as significant figures
if they are in the middle of a number.
0’s are NOT counted as significant figures
if you need them for place value
(the value of the number would change if you took them out)
Here are some examples:
2057
we need this 0 because it is
in the middle of a number.
It counts as a significant figure.
correct to 3 significant figures is
correct to 2 significant figures is
correct to 1 significant figure is

2060
2100
2000

f lex i p
we need these 0’s to keep
place value - so they are NOT
counted as significant figures.
We need them to show that the
2 is still worth 2000
ac k s
1
Decimals
we need this 0 because it is
in the middle of a number.
It counts as a significant figure
0.0105

0.0105
0.011
0.01

to 3 sig. figs is
to 2 sig. figs is
to 1 sig. fig is
we need these 0’s to keep
place value - so they are NOT
counted as significant figures
we need this 0 because it is
in the middle of a number.
It counts as a significant figure
3.08
to 3 sig. figs is
to 2 sig. figs is
to 1 sig. figs is
9990
to 3 sig. figs is
to 2 sig. figs is
to 1 sig. fig is

3.08
3.1
3
9990
10000
10000

you have to round this right up.
we need these 0’s to keep
place value - so they are NOT
counted as significant figures
f lex i p
A
How many significant figures does each of these numbers have?
(count the 0’s in the middle of a number, but not those at the end)
1)
2.01
2)
7000
3)
9.015
4)
6700
5)
30.7
6)
40
7)
3050
9)
67900
ac k s
2
Decimals
B
C
D
Have a go at putting these to
1)
1.7
2)
23
3)
946
4)
0.075
5)
0.1076
6)
39560
7)
0.999
1 significant figure
Have a go at putting these to
1)
1.75
2)
7.23
3)
946
4)
1.075
5)
0.1076
6)
39560
7)
0.999
2 significant figures
Have a go at putting these to
1)
1.754
2)
7.231
3)
94666
4)
1.075
5)
0.1076
6)
39560
7)
0.999
3 significant figures
f lex i p
Check your answers, then discuss with your tutor what you need to
work on next.
ac k s
3
Decimals
Answers
Significant Figures
A
1)
3
2)
1
3)
4
4)
2
5)
3
6)
1
7)
3
8)
3
B
1 significant figure
1) 2
2 significant figures
1) 1.8
2)
20
2)
7.2
3)
900
3)
950
4)
0.08
4)
1.1
5)
0.1
5)
0.11
6)
40000
6)
40000
7)
1
7)
1.0
3 significant figures
1) 1.75
7.23
3)
94700
4)
1.08
5)
0.108
6)
39600
7)
1.00
f lex i p
2)
ac k s
4