Question

40 is 0.08 of what number

Answer 1

40 = 0.08 x 
so x = 40/0.08 
x = 500 
40 is 8% of 500 

Answer 2

0.08 is 8%
0.08 × 100 = 8%

40 is 8% of what?
40 = 0.08x
$\frac{40}{0.08} = \frac{0.08x}{0.08}$
8 and 8 cancels out
x = 500

check
500 × 0.08 = 40