Mathematics
NULL
Medium
Question
Pipes P and Q fill a cistern in 12 and 16 minutes. Both open together; after how long should Q be closed so the tank is full in 9 minutes?
A
2 min
B
3 min
C
4 min
✓ Official correct answer
D
5 min
Community credibility
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A
2 min
No member explanations yet for this option.
B
3 min
No member explanations yet for this option.
C
4 min
No member explanations yet for this option.
D
5 min
No member explanations yet for this option.
Explanation
Let Q stay open t minutes: 9/12 + t/16 = 1 ⇒ t/16 = 1/4 ⇒ t = 4 min.