Question

Four pipes A, B, C and D can fill a tank with water in 15, 20, 30 and 60 hours respectively. Pipe A is opened at 4 a.m., B at 5 a.m., C at 6 a.m. and D at 7 a.m. When is the tank filled up completely?

Options

• 9:30 a.m.

• 10:00 a.m.

• 10:30 a.m.

• 11:00 a.m.

Answer 1

11:00 a.m.

Explanation:

Let the tank filled up after x hours when pipe A is opened

So, `"x"/15+("x"-1)/20+("x"-2)/30+("x"-3)/60=1`

4 x + 3(x − 1) + 2(x − 2) + (x − 3) = 60

10 x − 10 = 60

`"x"=70/10` = 70 hours.

Hence, the tank will be filled up at (4 + 7)

= 11 a.m