When is a number significant or not significant?

Answer 1

Any non-zero digit is significant. Example: 352.12 has 5 significant digits.

A zero is significant if it appears between non-zero digits. Example: 504.2 has 4 significant digits.

A zero is also significant when it appears after the decimal point, AFTER other digits. In this case, it was only added to indicate a significant digit. Example: 5.30 has 3 significant digits.

A zero after other numbers may or may not be significant. Use scientific notation to unambiguously indicate the number of significant digits. Example: 4500 has 2 significant digits. It may have 3 or 4 significant digits, but to be safe, assume 2 significant digits.

A zero is NOT significant if it comes after the decimal point, BEFORE any other digits. In this case, it is only used to put the digits in their proper place. Example: 0.0024 has 2 significant digits.