Question

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 used?

Answer 1

Pipes: Time:: Pipes: Time

  12  :    2x  ::   21  :  42

∴ By inverse proportion

12 × 42 = 21 × x

`⇒"x"=(12xx42)/21`

= 24 minutes