document.write( "Question 999139: . Bob takes 3 hours to mow a lawn. Al takes 4 hours. If they work together how long will it take? \n" ); document.write( "

Algebra.Com's Answer #616827 by jim_thompson5910(35256) $\"\"$ $\"About$

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x = time it takes Bob to mow the lawn by himself (no one else helps)
\n" ); document.write( "y = time it takes Al to mow the lawn by himself (no one else helps)
\n" ); document.write( "z = time it takes Bob and Al to mow the lawn if they work together. This is assuming they work the most efficiently and don't get in each other's way\r
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\n" ); document.write( "\n" ); document.write( "The values of x,y,z are times in hours\r
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\n" ); document.write( "\n" ); document.write( "We're given \"Bob takes 3 hours to mow a lawn. Al takes 4 hours\" so\r
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\n" ); document.write( "\n" ); document.write( "x = 3
\n" ); document.write( "y = 4
\n" ); document.write( "z = unknown but we can solve for it\r
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\n" ); document.write( "\n" ); document.write( "1/x + 1/y = 1/z
\n" ); document.write( "1/3 + 1/4 = 1/z
\n" ); document.write( "4/12 + 3/12 = 1/z
\n" ); document.write( "7/12 = 1/z
\n" ); document.write( "12/7 = z/1
\n" ); document.write( "z/1 = 12/7
\n" ); document.write( "z = 12/7\r
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\n" ); document.write( "\n" ); document.write( "If they work together, it takes exactly 12/7 hours which is approximately 1.714 hours (rounded to the nearest thousandth). \n" ); document.write( "

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