Pipes A, B and C together fill a tank in 4 hours. A alone takes 12 hours and B alone 15 hours. How long would C alone take?
Correct answer C. 10 hours
Explanation
C's rate = 1/4 − 1/12 − 1/15 = (15 − 5 − 4)/60 = 6/60 = 1/10 per hour, so C alone takes 10 hours.
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