Two pipes A and B together can fill a tank in 40 minutes. Pipe A is twice as fast as pipe B. Pipe A alone can fill the tank in:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 1 hour
$\text{Let rate of B}=r,\;\text{rate of A}=2r.$
$\text{Together rate}=3r.$
$3r=\frac{1}{40}.$
$r=\frac{1}{120}.$
$\text{Rate of A}=2r=\frac{1}{60}.$
$\text{Time of A}=\frac{1}{\frac{1}{60}}=60.$
$\text{Pipe A alone can fill the tank in }60\text{ minutes}.$