Question

how many significant digits are in the number 5.40

Answer 1

There are 3 significant digits in 5.40.

(To help understand): Sig figs are just a way of simplifying a number. 

Answer 2

Hey!
" 5.40 " have 3 significant figures

I'll explain it in an easy way.
The significant figures are "5" , "4" & "0" Since , zero comes after the decimal point. It can also be reported as a significant figure :)