Question 742195
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One pipe can fill a tank in 20 minutes, while another takes 30 minutes to fill the same tank. 
How long would it take the two pipes together to fill the tank?
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<pre>
First  pipe fills 1/20 of the tank volume per minute when works alone.

Second pipe fills 1/30 of the tank volume per minute when works alone.


Working together, both pipes fill  

    {{{1/20}}} + {{{1/30}}} = {{{3/60}}} + {{{2/60}}} = {{{5/60}}} = {{{1/12}}} 

of the tank volume per minute.


Hence, it will take 12 minutes for both pipes to fill the tank.    <U>ANSWER</U>
</pre>

Solved.


The answer in the post by @lynnlo is incorrect.