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Two pipes A and B can fill a tank independently in 20 and 30 minutes respectively. Both the pipes are opened simultaneously and after 6 minutes tap B is closed. Then the total time taken, in minutes,to fill the tank, is (assume that the tank is emptyinitially)
Solution:
Let total work be 60 units [LCM of 20,30]
A does 60 units in 20 minutes. Hence in 1 minute A does (60/20)units = 3 units.
B does 60 units in 30 minutes. Hence in 1 minute B does (60/30)units =2 units.
Total work in 1 minute = 5 units
Now, for the given scenario,
First,
A and B work for 6 minutes together @ 5 units/min
Work done = (5 x 6) units = 30
Work remaining =Total units of work - work done = 60-30 =30 UNITS .
Then,
A work alone @ 3 units/min.
Time taken = (Work remaining / speed) = 30/3 mins. = 10 minutes
Total time = 6 +10 = 16 minutes
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