document.write( "Question 677157: A large and a small heating unit are being used to heat the water of a pool. The large unit, working alone, requires 7 h to heat the pool. After both units have been operating for 3 h, the larger unit is turned off. The small unit requires 9 h more to heat the pool. How long would it take the small unit, working alone, to heat the pool \n" ); document.write( "

Algebra.Com's Answer #420775 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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A large and a small heating unit are being used to heat the water of a pool.
\n" ); document.write( " The large unit, working alone, requires 7 h to heat the pool.
\n" ); document.write( " After both units have been operating for 3 h, the larger unit is turned off.
\n" ); document.write( " The small unit requires 9 h more to heat the pool.
\n" ); document.write( " How long would it take the small unit, working alone, to heat the pool
\n" ); document.write( ":
\n" ); document.write( "let s = time required by the small unit to heat the pool alone
\n" ); document.write( "let the completed job = 1; (a warm pool)
\n" ); document.write( ":
\n" ); document.write( "A shared work equation; the small unit was on for 3 + 9 = 12 hrs
\n" ); document.write( ":
\n" ); document.write( " $\"3%2F7\"$ + $\"12%2Fs\"$ = 1
\n" ); document.write( "multiply by 7s to clear the denominators, resulting in:
\n" ); document.write( "3s + 7(12) = 7s
\n" ); document.write( "84 = 7s - 3s
\n" ); document.write( "84 = 4s
\n" ); document.write( "s = 84/4
\n" ); document.write( "s = 21 hrs, the small unit working alone
\n" ); document.write( ";
\n" ); document.write( ":
\n" ); document.write( "Check this:
\n" ); document.write( "3/7 + 12/21 =
\n" ); document.write( "9/21 + 12/21 = 21/21 = 1
\n" ); document.write( " \n" ); document.write( "

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