Question 1119209
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..., worked alone for 3 hours, his apprentice joins him and working together they complete the job 4 hours later....
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{{{(2/x)3+(2/x+1/x)4=1}}}

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{{{6/x+4(3/x)=1}}}

{{{18/x=1}}}

{{{highlight(x=18)}}}------the apprentice
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{{{18/2=highlight(9)}}}----time for plumber, one job