Question 988245
<pre>
Since it takes 1 faucet 6 hours to fill the tank, it will fill 
half the tank in 3 hours.

Then when three more faucets are opened, there will be 4 faucets 
filling it, so the second half of the tank will be filled 4 times
as fast as the first half was filled. So that will take only 1/4th
of the time it took to fill the first half, and 1/4th of 3 hours
is 3/4th of an hour or 45 minutes.  So it will take a total of
3 hours and 45 minutes.

Edwin</pre>