How many significant figures are in the number 0.00340500?

Answer 1

0.00340500 would be counted as 6 significant figures. The way you count is (from the left) the first non-zero digit would be the 1st significant digit. However, any zeros that appear behind that first significant digit is still counted not skipped. The value, rounded off to one significant figure, is 0.003. Do note that even if the number is exact, you have to add the extra zeros behind. For example, state 5 in 3 significant figures would mean the answer would be 5.00

The difference between 5 and 5.00 is that the two extra zeros indicate a level of precision that is 100 times greater. These zeros are not merely place holders.