Answers in correct significant digits

Significant digits is just how many digits is in the number, but '0' is a special case.
Example: 2542 --> 4 s.d.
13.47 --> 4 s.d.
9999000 --> 4 / 5 / 6 / 7(?) s.d.
843.560 --> 6 s.d.

..Yeah, I think that's it Hope it helps