If you add several numbers how many significant figures can the sum have?

Answer 1

The number whose farthest right significant digit determines it. Whatever place that digit is in is the last significant digit in the sum. For example: 433 + 150 + 3.67 + 8000 = 8586.67, but in sig figs this is only 9000, as the thousands digit is the lowest digit that can be represented.

Answer 2

The sum of numbers can have as many significant figures as the number with the least significant figures in the original numbers. For example, if you add numbers with 3, 4, and 5 significant figures, the sum will have 3 significant figures.