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Significant Figures
Measured Numbers
When you use a measuring tool is used to determine a quantity such as your height or weight, the numbers you obtain are called measured numbers.
Exact Numbers
Obtained when you count objects2 soccer balls
1 watch
4 pizzasObtained from a defined relationship
1 foot = 12 inches
1 meters = 100 cmNot obtained with measuring tools
Exact numbers are obtained by
1. Counting
2. Definition
3. Measuring
4. Counting & Definition
Measured numbers are obtained by
1. Measuring
2. Counting
3. Definition
Classify as exact or measured number : Gold melts at 1064
Celsius.1. Exact
2. Measured
Classify as exact or measured: 1 yard = 3 feet
1. Exact
2. Measured
Classify as exact or measured:A red blood cell with diameter 6 x
10 -4cm.1. Exact
2. Measured
Classify as exact or measured: There were six hats on the shelf.
1. Exact
2. Measured
Classify as exact or measured:A can of soda contains 355 mL of
soda. 1. Exact
2. Measured
Uncertainty in Measurement
The numbers reported in a measurement are limited by the measuring tool
Significant figures in a measurement include the known digits plus one estimated, or uncertain digit
This nail is 6.3 centimeters long for sure, but what exactly
is the value of the hundredths place
– 6.35, 6.36, 6.37?
“Significant figures in a measurement consist of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated.”
In the nail example, the hundredths place (3.36, the 6) is uncertain, or estimated.
A SIGNIFICANT FIGURE IS NOT ALWAYS CERTAIN – THE LAST DIGIT OF ANY MEASUREMENT IS ESTIMATED!!!
Rules For Significant Figures
1) All non-zero digits are significant
Examples:
35 2 significant figures
48.96 4 significant figures
How many significant figures in 896.76
A. 2
B. 3
C. 4
D. 5
Rules For Significant Figures
2) Zeros between numbers (sandwiched zeros) are all significant
Example:
304 – 3 significant digits
56.098 – 5 significant digits
How many significant figures in 1,043?
A. 1
B. 2
C. 3
D. 4
Rules For Significant Figures
3) Any zero appearing in front of a non-zero digit is NOT significant (regardless of a decimal)
Example:
0.876 – 3 significant digits
0.0056 – 2 significant digits
How many significant figures in 0.0008
A. 1
B. 3
C. 4
D. 5
Rules for significant figures
4) Zeros at the end of a number AND to the right of a decimal point are significant
Examples:
72.00 – 4 significant figures
7.000000000 – 10 significant figures
How many significant figures in 5.6000
A. 2
B. 4
C. 5
D. Help, I’m confused!
Rules For Significant Figures
5. A) Zeros at the end of the number WITHOUT a decimal place are NOT significant.
Example:
3,000 – 1 significant figure
560 – 2 significant figures
How many significant figures does 453,000 have?
A. 2
B. 3
C. 4
D. 6
Rules For Significant Figures
5 B) Zeros at the end of a number to the LEFT of a decimal point are significant
Example:
300.- Has three significant figures
4,000. – Has four significant figures
How many significant figures does 1,000. have?
A. 1
B. 2
C. 3
D. 4
How many sig figs does 305.00 have?
A. 2
B. 3
C. 5
D. Help! I’m confused!
How many sig figs does 0.009 have?
A. 1
B. 2
C. 3
D. 4
How many sig figs does 5,600.
A. 1
B. 2
C. 3
D. 4
Sig Figs in Calculations
A calculated answer cannot be more precise than the measuring tool.
A calculated answer must match the least precise measurement.
Significant figures are needed for final answers from 1) adding or subtracting
2) multiplying or dividing
Sig Figs and Addition/Subtraction
The answer has the same number of decimal places as the measurement with the fewest decimal places.
25.2 one decimal place
+ 1.34 two decimal places
26.54
answer 26.5 one decimal place
Round the answer to the correct number of significant
figures235.05 + 19.6 + 2.1 =
A) 256.75
B) 256.8
C) 257
Round the answer to the correct number of significant
figures 58.925 - 18.2
A) 40.725
B) 40.73
C) 40.7
Multiplying and Dividing with Sig Figs
Round (or add zeros) to the calculated answer until you have the same number of significant figures as the measurement with the fewest significant figures.
2.19 X 4.2
A. 9
B. 9.2
C. 9.198
4.311 ÷ 0.07
A. 61.58
B. 62
C. 60