If 30 men can do a piece of work in 20 hours, then in how many hours will 12 men do it?
18 hours
30 hours
40 hours
50 hours
Explanation:
Let the number of hours be x.
12 : 30 :: 20 : x
$\dfrac{20}{30}$ = $\dfrac{20}{x}$
x = $\dfrac{20 \times 30}{12}$ = 50