12 pipes, all of the same size, fill a tank in 42 minutes. How long will it take to fill the same tank, if 21 pipes of the same size are…
Answers:
Pipes : Time :: Pipes : Time
12 : 2x : 21 : 42
∴ By inverse proportion
12 × 42 = 21 × x
⇒ x = (12 × 42)/12 = 24 minutes