Question

Pipe A can fill a tank in 4 hours and pipe B can empty it in 5 hours. if both pipes are open at the same time, when will the tank be full?
pls explain with steps using direct or indirect variation.

Answer 1

Pipe A can fill the tank in 4 hours
and pipe B can empty it in 5 hours

Let the capacity of the tank be x ;
In 1 hour
Pipe A can fill 1/4 x and
Pipe B can empty 1/5 x

Therefore
In 1 hour tank filled
= 1/4 x - 1/5 x
= 9/20 x

In 1 hour ----> 9/20 x
In y hour ----> x
(9/20 x)/1 = x/y
9xy = 20x
y = 20/9
y = 20/9 hour
= 2 hr & 2/9 hr
= 2 hr & 120/9 min
= 2 hr 13 min 3/9 min
= 2 hr 13 min 20 sec

hence it will require 2 hours 13 min and 20 seconds for tank to full ...