document.write( "Question 433597: Chris can construct a robot on an erector set in 7 hours. His friend, Cristobal, can construct a robot using the same materials in 8 hours. How long would it take them to construct a robot if they both worked together? \n" ); document.write( "
Algebra.Com's Answer #300566 by stanbon(75887)\"\" \"About 
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Chris can construct a robot on an erector set in 7 hours. His friend, Cristobal, can construct a robot using the same materials in 8 hours. How long would it take them to construct a robot if they both worked together?
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\n" ); document.write( "Chris rate = 1/7 job/hr
\n" ); document.write( "Friend's rate = 1/8 job/hr
\n" ); document.write( "---
\n" ); document.write( "Together rate = 1/x job/hr
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\n" ); document.write( "Equation:
\n" ); document.write( "rate + rate = together rate
\n" ); document.write( "1/7 + 1/8 = 1/x
\n" ); document.write( "Multiply thru by 56x to get:
\n" ); document.write( "8x + 7x = 56
\n" ); document.write( "15x = 56
\n" ); document.write( "x = 3 11/56 hrs (time to do the job together)
\n" ); document.write( "---
\n" ); document.write( "x = 3 hr 12 minutes
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H. \n" ); document.write( "
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