2. Why Significant Figures
It enables us to have a clear idea of the
extent of the precision of the measuring
instrument being used or the measuring
method being employed.
3. Which figures are significant?
Rule #1: Non-zero
digits are always
significant
Rule #2: All zeroes
between significant
digits are significant
Rule #3: A final zero
or trailing zeroes
can only be
significant if there is a
decimal point or a
bar.
Let’s practice!
1234 kg
56, 789 ft
101 hr
134.001 kW
1230909 cm
10.0 s
100. s
$ 2050.00
7000 kW
0.0204000
4. Which figures are NOT
significant?
Zeroes are usually not significant in
the following instances:
Leading zeroes: zeroes before any
significant figure are never significant.
Ex. 0056, 0.00108
Trailing zeroes: zeroes after any
significant figure are not significant
when there are no decimal points or
bars
Ex. 76 000, 76 000., 76 00.0, 0.076000, 76
5. Infinite Number of Significant Figures
Counted Numbers
12 eggs in a dozen
There are 16 students in a class
Physical Constants
The value of π (3.14)
Avogadros’ Constant 6.02 x 1023
8. How many significant figures are in the
following measurements?
1. 30.0
2. 239
3. 0.890
4. 43.20
5. 1000
6. 34.42
7. 90.0
8. 0.0021
9. 5.400
10.0.0023
11.14.60
12.2 050
13.200.60
14.35
15.136.04
16.980.00
0
17.3.
18.570.0
19.0.700
20.12.040
21.460.13
22.15.010
23.19.80
24.0.0400
1
9. Adding and Subtracting
The result must be
rounded off to have
the same number
of decimal places
as the quantity with
the least number of
decimal places.
Examples:
0.0836 + 195.2 =
195.3
10.00
2.67 + 7.3333 =
3.5212 – 3.12 =
0.40
6 – 0.384 =6
10. Multiplying and Dividing
The result must be
rounded off to have Examples:
6.53
0.0390
the same number 0.0620 × 105.30 =
of significant
500
3.000 × 0.0130 =
figures as the
1000. / 2.010
=
quantity with the
9 / 0.765 =
least number of
significant figures.
13. Practice Work.
9. 0.556 × (40 - 32.5) = ?
10. 45 × 3.00 = ?
11. What is the average of 0.1707,
0.1713, 0.1720, 0.1704, and 0.1715?
5
2
12. 3.00 x 10 - 1.5 x 10 = ? (Give the
exact numerical result, and then express
that result to the correct number of
significant figures).