Question

A, B and C together can finish a piece of work in 4 days, A alone can do it in 9 days and B alone in 18 days How many days will be taken by C to do it alone

Answer 1

Let's time taken by C alone to complete the work in x days $\therefore$ $\frac{1}{4}=\frac{1}{9}+\frac{1}{18}+\frac{1}{x}$
$\frac{1}{x}=\frac{1}{4}-\frac{1}{9}+\frac{1}{18}$
$\frac{1}{x}=\frac{3}{36}$
$\frac{1}{x}=\frac{1}{12}$
$\Rightarrow x=12$ days