Question

Two pipes $A$ and $B$ can fill a tank in $20$ and $30$ minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?

• A. $10$ minutes
• B. $6$ minutes
• C. $12$ minutes
• D. $16$ minutes

Answer 1

The correct option is C $12$ minutes

Part filled by $A$ in $1$ minute $=\frac{1}{20}$
Part filled by $B$ in $1$ minute $=\frac{1}{30}$
Part filled by $(A+B)$ in $1$ minute $=\frac{1}{20}+\frac{1}{30}=\frac{1}{12}$
Hence, both pipes can fill the tank in $12$ minutes.