How many significant figures are in 2400?

Answer 1

There are two significant figures in 2400. You can "dump" the zeros in a case like this. If the number was 55,000, you could dump the zeros there, too, and there'd be two significant figures.

When working with a whole number (an integer), you can dump all the zeros to the left of the decimal until you reach the first nonzero digit. In the case of 343,505,000, you can only dump the 3 zeros, so there are 6 significant digits. If 12,005 is what you're working with, you can't dump any zeros and you have 5 significant figures. It's that simple with numbers that don't have any digits to the right of the decimal.
There are 2 significant figures in 2400; they are 2 and 4.