Question

A cistern can be filled by a tap in 4 hours while it can be emptied by another tap in 9 hours

Answer 1

Answer:

Step-by-step explanation:

When we have question like one is filling the tank and other is empting it, then we subtraction as,

Filled in 1 hour = 1/4

Empties in 1 hour = 1/9

Net filled in 1 hour = 1/4 - 1/9

= 5/36

So cistern will be filled in 36/5 hours i.e. 7.2 hours