Question

Pipe a and pipe b can fill a tank in 20 mins and 30 mins respectively. Both pipes open together but pipe a is closed after sometime and b filled remaining part of the tank in 15 mins. After how many mins did a close?

Answer 1

Answer:

Part filled in 4 minutes =4(1/15+1/20) = 7/15

Remaining part =(1-7/15) = 8/15

Part filled by B in 1 minute =1/20 : 8/15 :: 1:x

x = (8/15*1*20) = 1023min = 10min 40sec

The tank will be full in (4 min. + 10 min. + 40 sec.) = 14 min. 40 sec