Question

Tick (✓) the correct answer:
Two pipes can fill a tank in 20 minutes and 30 minutes respectively. If both the pipes are opened simultaneously, then hte tank will be filled in
(a) 10 minutes
(b) 12 minutes
(c) 15 minutes
(d) 25 minutes

Answer 1

(b) 12 minutes

$$\begin{gathered} \mathrm{First}\mathrm{pipe}\mathrm{can}\mathrm{fill}\mathrm{a}\mathrm{tank}\mathrm{in}20\mathrm{minutes}. \\ \mathrm{Second}\mathrm{pipe}\mathrm{can}\mathrm{fill}\text{the}\mathrm{tank}\mathrm{in}30\mathrm{minutes}. \\ \text{Part of tank filled by the first pipe in one minute}=\frac{1}{20} \\ \text{P}\mathrm{art\; of\; tank\; filled\; by\; the}\text{second}\mathrm{pipe\; in\; one\; minute}\frac{1}{30}\mathrm{Part\; of\; tank\; filled\; by}\text{both pipes}in\; one\; minute=\frac{1}{20}+\frac{1}{30}=\frac{5}{60}=\frac{1}{12}\text{Thus, it takes 12 minutes to fill the tank using both the pipes.} \end{gathered}$$