Pipes & Cistern
Important Instructions
A tank is filled by three pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The second pipe fills the tank 5 hours faster than the first pipe and 4 hours slower than the third pipe. The time required by the first pipe is:
Answer: C
Suppose, first pipe alone takes x hours to fill the tank .
Then, second and third pipes will take (x -5) and (x - 9) hours respectively to fill the tank.
(2x - 5)(x - 9) = x(x - 5)
x2 - 18x + 45 = 0
(x - 15)(x - 3) = 0
x = 15. [neglecting x = 3]
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A water tank is two-fifth full. Pipe A can fill a tank in 10 minutes and pipe B can empty in 6 minutes. If both the pipes are open, how long will it take to empty or fill the tank completely ?
Answer: A
There are two important points to learn in this type of question,
First, if both will open then tank will be empty first.
Second most important thing is,
If we are calculating filling of tank then we will subtract as (filling-empting)
If we are calculating empting of thank then we will subtract as (empting-filling)
So lets come on the question now,
Part to emptied 2/5
Part emptied in 1 minute =
1/6 - 1/10 = 1/15 => 1/15 : 25 :: 1: x =>25 × 15 = 6mins
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A cistern is filled by Pipe A and Pipe B together in 2.4 hours. Pipe A alone can fill the cistern at the rate of 100 litres per hour. Pipe B alone can fill the cistern in 4 hours. What is the capacity of the cistern?
Answer: B
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An electric pump can fill a tank in 3 hours. Because of a leak in the tank, it took 3 hours 30 min to fill the tank. In what time the leak can drain out all the water of the tank and will make tank empty ?
Answer: D
We can get the answer by subtracting work done by leak in one hour by subtraction of
filling for 1 hour without leak and with leak, as
Work done for 1 hour without leak = 1/3
Work done with leak =
So tank will be empty by the leak in 21 hours.
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A class eats 2/5 of chocolates on 1st day. On the 2nd day they eat 3/4 of the remainder. How many chocolates were there initially if still 75 chocolates are left?
Answer: A
Let there be 100 chocolates
215th of 100 40 chocolates eaten on first day
314th of the remaining 314th of (100-40) 45 chocolates
Chocolates left 100-40-45 15 chocolates
15 chocolates are left when 100 are there
75 chocolates are left when ? chocolates are there? = 500 Chocolates
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Pipes A and B can fill a tank in 20 hrs and 30 hrs respectively and pipe c can epmty the full tank in 40 hrs. If all the pipes are opened together, how much time will it take for the Tank to fill completely .. ?
Answer: C
No answer description available for this question.
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There is a leak at the bottom of a cistern. Due to this it takes 8 hours to fill the cistern. Had there not been a leak, it would take one hour less to fill the cistern. How much time does it take for the leak to completely empty the cistern?
Answer: C
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Pipe A can fill a tank 5 times faster than Pipe B and takes 32 minutes less than Pipe B to fill the tank. If both the pipes are opened together, then in how much time the tank would be full?
Answer: C
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Two outlet pipes A and B are connected to a full tank. Pipe A alone can empty the tank in 10 minutes and pipe B alone can empty the tank in 30 minutes. If both are opened together, how much time will it take to empty the tank completely?
Answer: B
Let the capacity of the tank be LCM(10, 30) = 30 units.
=> Efficiency of pipe A = 30 / 10 = 3 units / minute
=> Efficiency of pipe A = 30 / 30 = 1 units / minute
=> Combined efficiency of pipe A and pipe B = 4 units / minute
Therefore, time required to empty the tank if both pipes work = 30 / 4 = 7 minutes 30 seconds
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Two pipes A & B can fill a tank in 20 minutes and 30 minutes respectively. If both pipes are used together, how long will it take to fill the tank … ?
Answer: A
No answer description available for this question.
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