Addition
and subtraction with significant figures.
We will look at addition
but treat subtraction as addition with a negative sign in front.
When adding or subtracting
numbers, the answer should have less than or equal to the number of decimal
places as the number in the calculation with the least decimal places.
As shown on the right, the number with the least decimal places is 24.23.
So the answer should have only two decimal places.
If we are adding numbers
where some of the numbers have no digits after the decimal point, use
the rule mentioned above, but the answer has as many significant figures
as the number with the least significant figures.
Consider the calculation on
the right. The number 2,450,000 has three significant figures while 114.23
has five significant figures. The answer should therefore be expressed
with three significant figures. So we express 2,450,114.23 as 2,450,000
Consider the sum on the right.
The number 2,450 has three significant figures while 14.23 has 4 significant
figures. The answer should therefore be expressed with three significant
figures. So we express 2,464.23 as 2,460 by rounding down.
Consider the subtraction on
the right. The number 2,450,000 has three significant figures while 1,114.23
has 6 significant figures. The answer should therefore be expressed with
three significant figures. So we express 2,448,885.77 as 2,450,000 by rounding
up.
Take a deep breath
and try some examples.
Calculation
Number
with least significant figures
Number
of significant figures answer should expressed in.
