<PRE><B>Question 171680</B>
Three painters can finish painting a wall in 10 minutes. The first painter can finish a wall in 20 minutes and the second one can do it in 30 minutes. How long would it take the third painter to do the job alone. 
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1st painter DATA
Time = 20 min/job ; rate = 1/20 job/min
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2nd painter DATA:
Time = 30 min/job ; rate = 1/30 job/min
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3rd painter DATA:
Time = x min/job ; rate = 1/x job/min
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Together DATA:
Time = 10 min/job ;rate = 1/10 job/min
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EQUATION:
rate + rate + rate = together rate
1/20 + 1/30 + 1/x = 1/10

Multiply thru by 60x to get:
3x + 2x + 60 = 6x
x = 60 minutes (time for the 3rd painter to do the job)
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Cheers,
Stan H.</PRE>