document.write( "Question 801266: an empty tank can be filled with water in 20 mins using Pipe A or in 30 mins by Pipe B and the tank filled with water can be emptied of water in 40 mins by using Pipe C. When the three pipes A,B and c work together, approximately how long (in minutes) does it take to fill the empty tank with water? \n" ); document.write( "

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an empty tank can be filled with water in 20 mins using Pipe A or in 30 mins by Pipe B and the tank filled with water can be emptied of water in 40 mins by using Pipe C. When the three pipes A,B and c work together, approximately how long (in minutes) does it take to fill the empty tank with water?\r
\n" ); document.write( "\n" ); document.write( "let us consider tank filling or emptying as one job\r
\n" ); document.write( "\n" ); document.write( "Pipe A does 1/20 of the job in 1 minute\r
\n" ); document.write( "\n" ); document.write( "Pipe B does 1/30 of the job in 1 minute\r
\n" ); document.write( "\n" ); document.write( "Pipe C does 1/40 of the job in 1 minute\r
\n" ); document.write( "\n" ); document.write( "Pipe C is emptying\r
\n" ); document.write( "\n" ); document.write( "1/20 +1/30 -1/40 is the job done in 1 minute\r
\n" ); document.write( "\n" ); document.write( "7/120 of the job is done in 1 minute\r
\n" ); document.write( "\n" ); document.write( "120/7 minutes is taken to do 1 job\r
\n" ); document.write( "\n" ); document.write( "17.14 minutes \n" ); document.write( "

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