document.write( "Question 912380: A pool can be filled by one pipe in 20 hours and by a second pipe in 60 hours. How long will it take using both pipes to fill the pool? \n" ); document.write( "
Algebra.Com's Answer #553758 by Edwin McCravy(20054) $\"\"$ $\"About$
You can put this solution on YOUR website!
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document.write( "A pool can be filled by one pipe in 20 hours and by a second pipe in \r\n" );
document.write( "60 hours.  How long will it take using both pipes to fill the pool?\r\n" );
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document.write( "Make the chart below.  It is just like a D=RT chart except that\r\n" );
document.write( "D stands for \"DEEDS\" not \"DISTANCE\".  In other words, D stands\r\n" );
document.write( "for the number of DEEDS or JOBS or pools filled in each case.\r\n" );
document.write( "I'll use \"JOBS\".\r\n" );
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document.write( "               No of jobs     Rate in jobs per hour     Time in hours\r\n" );
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document.write( "1st pipe only                                                     \r\n" );
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document.write( "2nd pipe only                                                          \r\n" );
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document.write( "Both pipes                                                    \r\n" );
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document.write( "------------------------\r\n" );
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document.write( "We read:\r\n" );
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document.write( ">>...A pool can be filled by one pipe in 20 hours...<<\r\n" );
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document.write( "So that's 1 job in 20 hours. So we fill in 1 for the number\r\n" );
document.write( "of jobs which pipe 1 alone does and 20 for the number of hours.\r\n" );
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document.write( "               No of jobs     Rate in jobs per hour     Time in hours\r\n" );
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document.write( "1st pipe only       1                                        20\r\n" );
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document.write( "2nd pipe only                                                          \r\n" );
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document.write( "Both pipes \r\n" );
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document.write( "-------------\r\n" );
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document.write( "Next we read:\r\n" );
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document.write( ">>...A pool can be filled...by a second pipe in 60 hours...<<\r\n" );
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document.write( "That's 1 job in 60 hours for the 2nd pipe. So we fill in 1 for the number\r\n" );
document.write( "of jobs which the 2nd pipe does and 60 for the number of hours.\r\n" );
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document.write( "                                                  \r\n" );
document.write( "               No of jobs     Rate in jobs per hour     Time in hours\r\n" );
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document.write( "1st pipe only       1                                        20\r\n" );
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document.write( "2nd pipe only       1                                        60           \r\n" );
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document.write( "Both pipes                                                         \r\n" );
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document.write( "-----------------------\r\n" );
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document.write( "Now we read the question:\r\n" );
document.write( ">>...How long will it take using both pipes to fill the pool...<<\r\n" );
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document.write( "That asks how many hour would it that both pipes to do 1 job. So we \r\n" );
document.write( "let x be the number of hours it would take them to do 1 job, working\r\n" );
document.write( "together.  So we efill in 1 for the number of jobs and x for the \r\n" );
document.write( "number of hours. \r\n" );
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document.write( "               No of jobs     Rate in jobs per hour     Time in hours\r\n" );
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document.write( "1st pipe only       1                                        20\r\n" );
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document.write( "2nd pipe only       1                                        60\r\n" );
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document.write( "Both presses        1                                         x\r\n" );
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document.write( "----------------------\r\n" );
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document.write( "Now we fill in the rates by using the equivalent of\r\n" );
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document.write( "                    DISTANCE\r\n" );
document.write( "            RATE = ----------\r\n" );
document.write( "                      TIME\r\n" );
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document.write( "which is:\r\n" );
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document.write( "                       NUMBER of JOBS \r\n" );
document.write( "            RATE =   ----------------- \r\n" );
document.write( "                            TIME\r\n" );
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document.write( "               No of jobs     Rate in jobs per hour     Time in hours\r\n" );
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document.write( "1st pipe only       1                                     20\r\n" );
document.write( "2nd pipe only       1                                     60\r\n" );
document.write( "Both presses        1                                       x\r\n" );
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document.write( "Now we use the formula:\r\n" );
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document.write( "   Rate of 1st pipe + Rate of 2nd pipe = Rate of both pipes together\r\n" );
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document.write( "                           +  = \r\n" );
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document.write( "Can you solve that? You have to multiply through by the\r\n" );
document.write( "LCD of 60x.  If you can't solve it post again asking how.\r\n" );
document.write( "Answer: 15 hours.\r\n" );
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document.write( "Edwin
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