Question

8 pipes are required to fill a tank in 1 hr 20 min. How long will it take if only 6 pipes of the same type are used?

Answer 1

90 minutes or 1 hour 30 minutes

Explanation:

Time taken to fill t is inversely proportional to number of pipes. We can express this as t ∝
`(1)/(n)` where n is the number of pipes

We can also write this as t =
`(k)/(n)` where k is a constant

Using the data given 80 =
`(k)/(8)` (1)

For 6 pipes, if the time taken is T then

`T = (k)/(6)` (2)

Dividing (2) by (1) gives

`(T)/(80) = (k)/(6)` ÷
`(k)/(8)`

`(k)/(6)` ÷
`(k)/(8) = (k)/(6) (8)/(k) = (8)/(6)\\\\`

So

`(T)/(80) = (8)/(6)\\\\`

T =
`80 (8)/(6)` (multiplying both sides by 80

And this computes to 90 minutes or 1 hour 30 minutes