Give the number of significant figures of the population of a town which has approximately 5,020,700

Significant figures are the digits in a number that carry real meaning. The rules are simple: every non-zero digit counts, any zero sitting between two non-zero digits counts, but zeros at the end of a whole number (with no decimal point) are only place-holders, so they do not count.

Write out the number: 5 020 700. Start counting from the first non-zero digit on the left. That is 5 (counts), then 0 (it is between 5 and 2, so it counts), then 2 (counts), then 0 (it is between 2 and 7, so it counts), then 7 (counts). That gives 5 digits so far.

The last two zeros come after the 7 and there is no decimal point, so they are only holding the tens and units place. They are not significant. The count stops at 5 significant figures.

Note the difference: 7 would be the number of digits in total, not the number of significant ones. And 3 or 4 would mean you stopped counting the zeros trapped in the middle, which the rules say you must count.