Why does the number 54289.00 have seven significant figures and not five?

Answer 1

The two zeros after the decimal point indicate that the number is accurate to one in a hundred.

If there were 5 significant digits the true value would lie between 54288.5 and 54289.5 but the above representation tells you that is cannot be more than 54289.1, for example. In fact, the true value lies between 54288.995 and 54289.005