Rule
1.
If the digit following the last significant figure is less than 5,
the last significant figure remains unchanged. The digits after
the last significant figure are dropped.
Example:
Round 23.437 to three significant figures.
Answer:
23.4
Explanation:
4 is the last significant figure. The next number is 3. 3 is less than
5. Thus, 4 remains unchanged and 37 is dropped.
Rule
2.
If the digit
following the last significant figure is greater than 5, then 1
is added to the last significant figure. The digits after the last
significant figure are dropped.
Example:
Round 5.383 to two significant figures.
Answer:
5.4
Explanation:
3 is the last significant figure. The next number is 8. 8 is greater
than 5. Thus, 1 is added to 3 making it 4. The 83 is dropped.
Rule
3.
If the digit
following the last significant figure is 5, then 1 is
added to the last significant figure if the last significant figure
is odd. If the last significant figure is even, it remains unchanged
and the digits after the last significant figure are dropped.
Example
1: Round 3.35
to two significant figures.
Answer: 3.4
Explanation: 3 is the last significant figure. The next number
is 5. 3 is an odd number. Odd numbers round up when the following number
is a 5.
Example
2: Round 7.25
to two significant figures.
Answer: 7.2
Explanation: 2 is the last significant figure. The next number
is 5. 2 is an even number. Even numbers remain unchanged when they are
followed by a five. The 5 is dropped.
