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

Answer:

90 minutes or 1 hour 30 minutes

Step-by-step explanation:

Time taken to fill t is inversely proportional to number of pipes. We can express this as t ∝ $\frac{1}{n}$ where n is the number of pipes

We can also write this as t = $\frac{k}{n}$ where k is a constant

Using the data given 80 = $\frac{k}{8}$    (1)

For 6 pipes, if the time taken is T then  

$T = \frac{k}{6}$      (2)

Dividing (2) by (1) gives

$\frac{T}{80} = \frac{k}{6}$ ÷ $\frac{k}{8}$

$\frac{k}{6}$ ÷ $\frac{k}{8} = \frac{k}{6} \frac{8}{k} = \frac{8}{6}$

So  

$\frac{T}{80} = \frac{8}{6}$

T = $80 \frac{8}{6}$  (multiplying both sides by 80

And this computes to 90 minutes or 1 hour 30 minutes