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Pipe A fills a tank of capacity 700 liters at the rate of 40 [#permalink]
29 Apr 2010, 10:40

2

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Difficulty:

5% (low)

Question Stats:

76% (02:45) correct
23% (01:03) wrong based on 13 sessions

Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?
_________________

But there’s something in me that just keeps going on. I think it has something to do with tomorrow, that there is always one, and that everything can change when it comes. http://aimingformba.blogspot.com

Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?

In one cycle they fill 40+30-20 = 50 liters

700 = 50*n => n = 14 here n = number of cycles.

total time = 14*3 = 42 as in one cycle there are 3 minutes.

thus 42 minutes....whats the OA?
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Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?

In three minutes net gain is 40+30-20=50 liters;

After 13 cycles (13*3=39 minutes) net gain will be 13*50=650 liters.

Then in 1 minute pipe A will add 40 liters, 10 liters to be filled;

Then to fill 10 liters pipe B will need 10/30=1/3 min.

So total time 39+1+\frac{1}{3}=40\frac{1}{3} min.
_________________

Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?

In three minutes net gain is 40+30-20=50 liter;

After 13 cycles (13*3=39 minutes) they fill 13*50=650 liters.

Then in 1 minute pipe A will add 40 liters, 10 liters to be filled;

Then to fill 10 liters pipe B will need 10/30=1/3 min.

divide 700/50... u get 14 cycles. but u know that before 20 then take away the last cycle. so u have 13 cycles (39 mins), where the tank is 650 ls full. let's take the 14th cycle. the first minute, the tank gets to 650 + 40 = 690ls. there's only 10 ls left to fill the tank. the second step of the cycle is pipe B that fills 30 ls in 1 minute. since we only need 10 ls, we only need 1/3rd of a minute.

so we have 13 cycles plus 1 min of pipe A and 1/3rd minute of pipe B.
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Re: Pipe A fills a tank of capacity 700 liters at the rate of 40 [#permalink]
07 Jun 2013, 05:17

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I still dont get it.... i mean I understand everything but the logic as to why we should NOT consider 14 cycles as we have already done the filling in and filling out calculations.

Re: Pipe A fills a tank of capacity 700 liters at the rate of 40 [#permalink]
07 Jun 2013, 05:28

1

This post received KUDOS

samheeta wrote:

I still dont get it.... i mean I understand everything but the logic as to why we should NOT consider 14 cycles as we have already done the filling in and filling out calculations.

The sequence of the events is: Pipe A adds 40 liters/m Pipe B adds 30 liters/m Pipe C subtracts 20 liters/m =NET +50

When you have done 13 circles in 40 minutes, there are 650 liters and 50 to go. Now the squence repeats Pipe A adds 40 liters/m----50-40=10 liters to go and 1 minute more added Pipe B adds 30 liters/m----so 10 liters will be filled in \frac{1}{3} of a minute STOP Pipe C subtracts 20 liters/m

Tot time 40 minutes and \frac{1}{3} _________________

It is beyond a doubt that all our knowledge that begins with experience.

Re: Pipe A fills a tank of capacity 700 liters at the rate of 40 [#permalink]
20 Nov 2013, 09:53

aiming4mba wrote:

Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?

tricky tricky! I had gotten 42 minutes at first, not realizing it would actually finish at 700, but also hit 700 before, 1/3 of the way into B's cycle on the 20th go around.

gmatclubot

Re: Pipe A fills a tank of capacity 700 liters at the rate of 40
[#permalink]
20 Nov 2013, 09:53