Question 1207433: In a laundry sink, the hot water tap lets out 3 litres of water every minute. The cold water tap lets out 4 litres of water every minute. If the sink is left unplugged, 2 litres of water are drained every minute. With the sink unplugged, I turn on the cold water tap. Three minutes later, I turn on the hot water tap as well. I leave both taps running for another 2 minutes before both taps are turned off. How long do I now have to wait before the sink is completely drained?
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(52792)   (Show Source):
You can put this solution on YOUR website! .
In a laundry sink, the hot water tap lets out 3 litres of water every minute.
The cold water tap lets out 4 litres of water every minute.
If the sink is left unplugged, 2 litres of water are drained every minute.
With the sink unplugged, I turn on the cold water tap.
Three minutes later, I turn on the hot water tap as well.
I leave both taps running for another 2 minutes before both taps are turned off.
How long do I now have to wait before the sink is completely drained?
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Many words, but the idea of solution is simple -
accurately count the balance of water.
During first three minutes, the inflow is 4*3 liters = 12 liters (the cold water tap);
the outflow is 2*3 liters = 6 liters (the sink);
the net inflow is 12 - 6 = 6 liters.
During next two minutes, the inflow is 4*2 + 3*2 = 14 liters (both the cold water tap and hot water tap;);
the outflow is 2*2 = 4 liters (the sink);
the net inflow is 14 - 4 = 10 liters.
After 3+2 = 5 minutes both taps are turned off.
Now only the sink is on. It drains 6+10 = 16 liters at the rate of 2 liters per minute.
So, you need wait 16/2 = 8 minutes to get the sink completely drained.
Solved.
Just boldly go forward and count everything in your path.
There is no need for bright ideas.
You only need to know right words and use them properly in order for seem smart.
Answer by greenestamps(13200)  (Show Source):
You can put this solution on YOUR website!
The cold water tap, filling the sink at the rate of 4 liters per minute, is on for 3+2=5 minutes, putting 4*5=20 liters of water in the sink.
The hot water tap, filling the sink at the rate of 3 liters per minute, is on for 2 minutes, putting 3*2=6 liters of water in the sink.
So a total of 20+6=26 liters of water was put into the tank.
The drain empties the tank at the rate of 2 liters per minutes; the amount of time it takes to drain 26 liters is 26/2 = 13 minutes.
The drain is open for the 5 minutes while the taps are putting water into the sink; the number of minutes it takes to empty the sink after the taps are turned off is 13-5=8.
ANSWER: 8 minutes
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