Three pipes A B and C is attached to a cistern A can fill it in 20 minutes and B can fill it in 30 m...........

Quantitative Aptitude ( CCS) Pipes&cistern

Three pipes A, B and C is attached to a cistern. A can fill it in 20 minutes and B can fill it in 30 minutes. C is a waste pipe. After opening both the pipes A and B, Riya leaves the cistern to fill and returns when the cistern is supposed to be filled. But she found that waste pipe C had been left open, she closes it and now the cistern takes 5 minutes more to fill. In how much time the pipe C can empty the full cistern?

26.8 minutes

25.8 minutes

27.8 minutes

28.8 minutes

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Explanation:

Answer & Explanation
Answer – d) 28.8 minutes
Explanation :
The tank supposed to be filled in (30*20)/50 = 12 minutes
so, (1/20 + 1/30)*12 – 12/C + (1/20 + 1/30)*5 = 1 (A and B work for 12 minutes and also C work for 12 minutes and then A and B takes 5 more minutes to fill the tank)
solve for C, we will get C = 144/5 = 28.8