a) 20 days
b) 30 days
c) 10 days
d) 15 days

Answer: a
Explanation
$$\eqalign{ & {\text{15 men}} = {\text{20 days}} \cr & {\text{300 men}} = 1{\text{ days}}…..{\text{(i)}} \cr & {\text{24 women}} = {\text{20 days}} \cr & {\text{480 men}} = 1{\text{ days}}……{\text{(ii)}} \cr & {\text{Compare equation (i) and (ii)}} \cr & {\text{300 men}} = 480{\text{ women}} \cr & {\text{5 men}} = 8{\text{ women}}…..{\text{(iii)}} \cr & {\text{10 men}} + 8{\text{ women}} = ? \cr & {\text{10 men}} + {\text{5 men}} = ? \cr & 15\,{\text{men}} = ? \cr} $$
$${\text{15 men}} \times {\text{20 days}}$$     = $${\text{15 men}}$$  $$ \times $$ $$x{\text{ days}}$$
$$x$$ = 20 days