5250000 determine the number of significant figures

here are three rules on determining how many significant figures are in a number: Non-zero digits are always significant. Any zeros between two significant digits are significant. A final zero or trailing zeros in the decimal portion ONLY are significant.

3 significant figures

Explanation:

We only count the numbers that aren't zero, which is 3. If the number were instead a decimal then we would count all of the numbers including the zeros since they are after the non-zero numbers