Question

If 3 men or 6 boys can finish a work in 20 days, how long will 4 men and 12 boys take to finish the same work?

Answer 1

3 men = 6 boys
4 men $=\frac{6}{3}\times 4$
= 8
Total boys in second case:
= 4 men + 12 boys
= 8 + 12
= 20 boys
6 boys can do a piece of work in 20 days.
Then let 20 boys will do the same work in x days.
$\therefore 6:20::20;x$
(More boys, less days)
$\Rightarrow 6:20::x:20$
(By inverse proportion)
$x=\frac{20\times 6}{20}$
= 6 days
$\therefore$ They will do the work in 6 days.