SOLUTION: Mark can overhaul an engine in 20 hours and Phil can do the same job by himself in 30 hours. If they both work together for a time and then Mark finishes the job by himslef in 5

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Question 142784This question is from textbook
: Mark can overhaul an engine in 20 hours and Phil can do the same job by himself in 30 hours. If they both work together for a time and then Mark finishes the job by himslef in 5 hours. How long did they work together? This question is from textbook

Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
Mark does 1/4 (5/20) of the job alone, so together he and Phil do 3/4

let x= time together

x/20+x/30=3/4 __ multiplying by 60 (LCD) __ 3x+2x=45 __ 5x=45 __ x=9