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:

1 hour

The correct answer is Option (1) → 1 hour

$\text{Let rate of B}=r,\;\text{rate of A}=2r.$

$\text{Together rate}=3r.$

$3r=\frac{1}{40}.$

$r=\frac{1}{120}.$

$\text{Rate of A}=2r=\frac{1}{60}.$

$\text{Time of A}=\frac{1}{\frac{1}{60}}=60.$

$\text{Pipe A alone can fill the tank in }60\text{ minutes}.$