1.

Two pipes can fill a tank in 10 hours and 12 hours respectively, while a third pipe empties the full tank in 20 hours. If all the three pipes operate simultaneously, in how much time the tank will be filled?1). 7 hrs2). 8 hrs3). 7 hrs. 30 min.4). 8 hrs. 30 min.

Answer»

Time taken by A , B and C to fill/empty the tank completely = 10 , 12 and 20 hours respectively

Hence part of tank filled by A, B and EMPTIED by C in 1 hour = 1/10, 1/12 and 1/20 respectively

Part of tank filled by all 3 pipes in 1 min $(= \FRAC{1}{{10}} + \frac{1}{{12}}\; - \frac{1}{{20}})$

$(= \frac{6}{{60}}\; + \frac{5}{{60}}-\frac{3}{{60}})$

$(= \frac{8}{{60}})$

= 2/15

Hence it will take 15/2 hours IE 7 hours and 30 mins to completely fill the tank


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