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Deepak Chetri

· started a discussion

· 1 Months ago

stuck in the middle of the solution (Question: 83303.0 )

When the pipes are opened how it came 1/20-1/30 please explain that part

Question:

Two pipes A and B can fill a tank in 36 minutes and 45 minutes, respectively. Another pipe C can empty the tank in 30 minutes. First A and B are opened. After 7 minutes, C is also opened. Now,the tank is filled in the next:

Options:
A) 39 minutes
B) 46 minutes
C) 40 minutes
D)

45 minutes


Solution:

Ans:(a)

Pipe A can fill empty tank in 30 min.

Pipe A can fill the tank = 100/36 = 2.77% per minute.

Pipe B can fill empty tank in 45 min.

Pipe B can fill the tank = 100/45 = 2.22% per min.

A and B can together fill the tank,

= (2.77 + 2.22)= 5% per minute.

So, A and B can fill the tank in 7 min.,

= 7*5 = 35% of the tank.

Rest tank to be filled = 100 - 35 = 65%.

C can empty the full tank in 30 min.

C can empty the tank = 100/30 = 3.33% per min.

C is doing negative work i.e. emptying the tank.

A, B and C can together fill the tank,

= 2.77% + 2.22% - 3.33% = 1.67% tank per minute.

So, A, B and C will take time to fill 65% empty tank,

= 65/1.67 = 39 min. (Approx.)

Knowledge Expert

· commented

· 1 Months ago

Pipe A can fill empty tank in 30 min.
Pipe A can fill the tank = 100/36 = 2.77% per minute.
Pipe B can fill empty tank in 45 min.
Pipe B can fill the tank = 100/45 = 2.22% per min.
A and B can together fill the tank,
= (2.77 + 2.22)= 5% per minute.
So, A and B can fill the tank in 7 min.,
= 7*5 = 35% of the tank.
Rest tank to be filled = 100 - 35 = 65%.
C can empty the full tank in 30 min.
C can empty the tank = 100/30 = 3.33% per min.
C is doing negative work i.e. emptying the tank.
A, B and C can together fill the tank,
= 2.77% + 2.22% - 3.33% = 1.67% tank per minute.
So, A, B and C will take time to fill 65% empty tank,
= 65/1.67 = 39 min. (Approx.)
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