Mathematics
NULL
Medium
Question
Two taps fill a cistern in 10 and 15 minutes; with the waste pipe open they fill it in 18 minutes. Time for the waste pipe alone to empty it?
A
7 min
B
13 min
C
23 min
D
9 min
✓ Official correct answer
Community credibility
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A
7 min
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B
13 min
No member explanations yet for this option.
C
23 min
No member explanations yet for this option.
D
9 min
No member explanations yet for this option.
Explanation
1/10 + 1/15 − 1/w = 1/18 ⇒ 1/w = 1/9 ⇒ w = 9 min.