Adding and Subtracting with proper precision
What is the perimeter of an object with sides of length 10.42 m, 13.372 m, 12.0 m, and 11.05 m?
10.420
10.42 m
13.372 m
12.000
m
12.0
+11.050
+11.05 m
46.842 m
 46.8 m
Keep in your answer everything you are
sure of plus one estimated digit.
The first estimated digit is the tenths
place, so round to the nearest tenth.
Notice the precision (number of
decimal places) of each original
measurement and the answer.
12.0 m is the least precise measurement. It is
only precise to the nearest tenth. Notice that
the answer is also precise to the nearest tenth.
Adding and Subtracting with proper precision
What is the perimeter of an object with sides of length 14.4 m, 13 m, 12.25 m, and 10. m?
14.4
14.40
13
13.00
12.25
+10.
+10.00
m
m
m
m
49.65 m
 50. m
Keep in your answer everything you are
sure of plus one estimated digit.
Round to the nearest one.
Adding and Subtracting with proper precision
What is the perimeter of an object with sides of length 14.4 m, 13 m, 12.25 m, and 10. m?
14.4
14.40
13
13.00
12.25
+10.
+10.00
Keep in your answer everything you are
sure of plus one estimated digit.
m
m
m
m
13 m and 10. m are the least precise
measurements. They are both only precise to
the nearest one. Notice that the answer is also
precise to the nearest one.
49.65 m
 50. m
Rules for adding and subtracting with Significant Figures
1. Change the units of all measurements so that all
measurements are expressed in the same units.
Notice: No counting of
significant figures!
2. Add or subtract.
3. Round the answer to the least precise
original measurement. (Round the answer to
the least number of decimal places in any
measurement.)