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Pipe A, pipe B and pipe C together can fill a tank in 20 minutes, but because of the leak all three pipes take 10 minutes more time to fill the tank completely. Find the time in which leak can empty the full tank.
40 min
60 min
30 min
45 min
60 min
Use the formula TleakтАЛ=T2тАЛтИТT1тАЛT1тАЛ├ЧT2тАЛтАЛ where T1тАЛ=20 and T2тАЛ=30. Calculation: (20├Ч30)/(30тИТ20)=600/10=60.
Combined rate of Pipe A, B, and C = 1/20 tank/min. Time taken with leak = 20 + 10 = 30 minutes.
TnetтАЛ1тАЛ=TfillтАЛ1тАЛтИТTleakтАЛ1тАЛ
Use the formula TleakтАЛ=T2тАЛтИТT1тАЛT1тАЛ├ЧT2тАЛтАЛ where T1тАЛ=20 and T2тАЛ=30. Calculation: (20├Ч30)/(30тИТ20)=600/10=60.
Students often use 10 minutes instead of the total time (20 + 10 = 30) for the leak-affected process.
Define rates
Let RfillтАЛ be the filling rate of pipes (A+B+C) and RleakтАЛ be the emptying rate of the leak. The filling rate is 1/20 tank/min.
RfillтАЛ=201тАЛ
Calculate effective rate
With the leak, the total time is 20+10=30 minutes. The effective filling rate is 1/30 tank/min.
ReffтАЛ=301тАЛ
Find leak rate
Using the relation ReffтАЛ=RfillтАЛтИТRleakтАЛ, we get RleakтАЛ=RfillтАЛтИТReffтАЛ=1/20тИТ1/30.
RleakтАЛ=603тИТ2тАЛ=601тАЛ
Final answer
The time required for the leak to empty the full tank is the reciprocal of the leak rate.
TleakтАЛ=60┬аminutes
B is correct because the leak reduces the effective net rate to 1/30 tank per minute, resulting in a time of 60 minutes to empty the tank.
This concept of 'Net Rate = Gross Rate - Loss Rate' is identical to relative speed problems where VnetтАЛ=V1тАЛтИТV2тАЛ for objects moving in opposite directions.