Question

Two pipes can fill a tank in 20 minutes and 30 minutes respectively. If both the pipes are opened simultaneously, then the tank will be filled in

• A. $10$ minutes
• B. $12$ minutes
• C. $15$ minutes
• D. $25$ minutes

Answer 1

Answer: (B)

$12$ minutes

Part of tank filled by 1st pipe in 1 minute $=\frac{1}{20}$
Part of tank filled by 2nd pipe in 1 minute $=\frac{1}{30}$
$\therefore$ Part of tank filled by both the pipes in 1 minute $=\left(\frac{1}{20}+\frac{1}{30}\right)=\frac{5}{60}=\frac{1}{12}$
Time taken to fill the tank $=12$ minutes.