Multiple choice

A, B and C together can fill a tank in 6 hours. After 2 hr. pipe C will be closed and A, B together fill the remaining tank in 7 hours. In what time C can fill the empty tank?

  1. 15 hr

  2. 20 hr

  3. 14 hr

  4. 18 hr

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Total work = 1 tank. A+B+C rate = 1/6 per hour. In 2 hours, 1/3 tank filled. Remaining 2/3 filled by A+B in 7 hours, so A+B rate = (2/3)/7 = 2/21. C's rate = 1/6 - 2/21 = 7/42 - 4/42 = 3/42 = 1/14. C alone takes 14 hours.