document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1163890>Question 1163890</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A pool has 1 intake pipe and 3 drainage pipes. It takes 20 minutes to fill up the pool. If 1 drainage pipe is used, it takes 45 minutes to drain the pool. Now 2/3 of the pool is filled. If all 4 pipes are turned on, how long does it take to have 2/5 of the pool filled? </SPAN>\n" );
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document.write( "The intake pipe fills 1/20 of the pool each minute.<br><BR>\n" );
document.write( "Each drain pipe empties 1/45 of the pool each minute; the three drain pipes together empty 3/45 = 1/15 of the pool each minute.<br><BR>\n" );
document.write( "If all 4 pipes are open, the fraction of the pool that is emptied each minute is 1/15-1/20 = 4/60-3/60 = 1/60.<br><BR>\n" );
document.write( "Starting with the pool 2/3 full and going until it is 2/5 full, the fraction of the pool that is emptied is 2/3-2/5 = 10/15-6/15 = 4/15.<br><BR>\n" );
document.write( "The number of minutes required to empty 4/15 of the pool at the rate of 1/60 of the pool per minute is (4/15)/(1/60) = (16/60)/(1/60) = 16.<br><BR>\n" );
document.write( "ANSWER: 16 minutes<br><BR>\n" );
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