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Two pumps P & Q can fill a tank in 12 mins and 15 mins respectively while a third pipe R can empty the full tank in 6 mins. P & Q kept open for 5 mins in the beginning and then R is also opened. In what time is tank emptied? A) 30mins B) 35mins C) 40mins D) 45 mins
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1 Answer

D

Part filled in 5 min = 5(1/12 +1/15)

= 5*9/60 = ¾

Part emptied in 1 min when all the pumps are opened,

= 1/6 – (1/12 + 1/15)

= 1/6 – 3/20

= 1/60

Now 1/60 is part emptied in 1 min

Therefore ¾ part will be emptied in 60 * ¾ = 45 mins
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