Question:
Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
[A].5 min.
9 min.
10 min.
15 min.
Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in just half an hour, if the B is turned off after:
[A].
[B].
[C].
[D].
Answer: Option B
Explanation:
Let B be turned off after x minutes. Then,
Part filled by (A + B) in x min. + Part filled by A in (30 -x) min. = 1.
x | 2 | + | 1 | + (30 – x). | 2 | = 1 | ||
75 | 45 | 75 |
11x | + | (60 -2x) | = 1 | |
225 | 75 |
11x + 180 – 6x = 225.
x = 9.