SOLUTION: A water tank can be filled by three pipes separately in 20,30 and 6o minutes respectively.In how many minutes can it be filled by the three pipes acting together?

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Question 1099899: A water tank can be filled by three pipes separately in 20,30 and 6o minutes respectively.In how many minutes can it be filled by the three pipes acting together?
Found 2 solutions by ikleyn, greenestamps:
Answer by ikleyn(53751) About Me  (Show Source):
You can put this solution on YOUR website!
.
1%2F20 of the job per minute is the rate of the 1-st tube.

1%2F30 of the job per minute is the rate of the 2-nd tube.

1%2F60 of the job per minute is the rate of the 3-rd tube.

The combined rate of work of all three tubes working together is  

    1%2F20+%2B+1%2F30+%2B+1%2F60 = 3%2F60+%2B+2%2F60+%2B+1%2F60 = 6%2F60 = 1%2F10 of the job per minute.


Hence, it will take 10 minutes for the three tubes to fill the tank working together.


Answer by greenestamps(13330) About Me  (Show Source):
You can put this solution on YOUR website!

Here is an alternative method of solution for this kind of problem which avoids working with fractions....

Consider the 60 minutes it takes the third pipe to fill the tank.

The first pipe could fill 3 of the tanks in those same 60 minutes.
The second pipe could fill 2 of the tanks in the 60 minutes.

So all working together, the three pipes could fill 1+3+2 = 6 tanks in 60 minutes.

And that means they could fill the one tank in 10 minutes.