A, B, C are pipes attached into a cistern. A and B can fill it in 20 and 30 minutes respectively, while C can empty it in 15 minutes. If A, B and C be kept open successively for 1 minute each, how soon will the cistern be filled ?
(a) 2 hr 44 min
(b) 2 hr 40 min
(c) 2 hr 47 min
(d) 2 hr 37 min
(e) None of these
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(1/20+1/30-1/15)=1/60. which is in 3 min.
therefore, 1-(1/20+1/30) = 55/60. so, 55/60 of cistern filled in (3*55=165) min.
now, 5/60 of the cistern remained to be filled.
A will fill 1/20 portion in 1 min.
remaining (5/60 - 1/20) or 1/30 in 1 min.
therefore time reqd is. (165+1+1)= 167 min.
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