Question

A tap can fill a cistern in 3 hours and another can empty it in 9 hours. If both the taps are opened simultaneously, how much time it will take to fill the tank?

A)11/2 hours
B)5 hours
C)9/2 hours
D)4 hours ​

Answer 1

Answer:

c - 9/2 hours

Step-by-step explanation:

First tap is filling in 3 hours

Therefore in 1 hour it will fill (1/3) of the tank and

Second is emptying it in 9 hours

Therefore in 1 hour it will remove (1/9) of the tank .

since first tap is filling and second tap is removing water

Therefore

( 1/3 ) - ( 1/9 )= ( 2/9) of the tank

Now,

Since in one hour both taps are filling ( 2/9 ) of the tank

Therefore in ( x ) hours it will filling total tank means ( 9/9 )= 1 of the tank

Therefore ( x ) = 1 ÷ (2/9) = 9/2 hours.

...Ans