IBPS SO Prelims Exam Model Paper 7

Given:
Time taken by pipe A and pipe B to fill a tank = 6 mins
A takes 5 minutes less than B to fill the tank
Calculation:
Let the time taken by pipe A to fill the tank be x minutes
Then, Time is taken by pipe B to fill the tank = x + 5
So,

1

x

+

1

(x+5)

=

1

6

⇒

(2x+5)

x(x+5)

=

1

6

⇒ 12x + 30 =x2 + 5x
⇒ x2 - 7x - 30 = 0
⇒ x2 - 10x + 3x - 30 = 0
⇒ x(x - 10) + 3(x - 10) = 0
⇒ (x - 10)(x + 3) = 0
⇒ x = -3, is not possible
So, x = 10
Time taken by B to fill the tank = (10 + 5) minutes
⇒ 15 minutes
∴ Time taken by B alone to fill the tank in 15 minutes