Significant figures of a number are the digits that carry meaning contributing to its precision of measurement.

Which number is more precise?
220
217

Scientific Notation
Method of expressing numbers in terms of a decimal number between 1 and 10 multiplied by a power of 10. Example:
10,492 = 1.0492 x 10^4

rules

• Non-zero digits are always significant.
• Any zeros between two significant digits are significant.
• Final zeros in the decimal portion only are significant.
• Zeros to the right of a decimal point and the left of a significant digit are NOT significant.
• All scientific notation numbers are significant.

hint: start counting significant figures at the first non-zero digit

How many sig figs.

• 1123
• 0.054
• 760
• 1010
• 1010.0
• 1.2340 x 10^4

For addition and subtraction, look at the decimal portion (to the right of the decimal point) of the numbers ONLY. Here is what to do:

1) Count the number of significant figures in the decimal portion of each number in the problem. (The digits to the left of the decimal place are not used to determine the number of decimal places in the final answer.)
2) Add or subtract in the normal fashion.
3) Round the answer to the LEAST number of places in the decimal portion of any number in the problem.

The following rule applies for multiplication and division:

The LEAST number of significant figures in any number of the problem determines the number of significant figures in the answer.
This means you MUST know how to recognize significant figures in order to use this rule.

rounding hint:
if rounding to one significant figure draw a line after the first non-zero digit, round
ex: round 5341 to one sig fig
5/341 -> 5000
or round it to two sig fig
53/41-> 5300