How do you figure how many significant figures a number has?

Answer 1

Generally speaking, one can't have more significant figures in the answer to a mathematical equation than the least number of significant figures of all the values used to generate that equation.

6*6=40

6.0*6.0=36

For example: 1.1/2.3=0.478260869... But it doesn't make sense for the answer to have more significant figures than 2: 0.48. The point of significant figures is that the precision of the answer should reflect the precision of the factors that led to the answer.

For example, suppose you were trying to measure the length of two pieces of string, with a ruler graduated down to millimeters. Lets say you wanted the sum of the length of the two strings. It would not make sense to express the sum in nanometers, because the precision of the measurements was in millimeter level. It would also be incorrect to express the sum in centimeters even if the result was a number with one or more trailing zeros, the measurements were accurate to 1 millimeter.

374mm + 626mm = 1000mm

NOT 1 meter nor 100cm (but 1.000 meter, or 100.0cm)