<PRE><B>Question 1203763</B>
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20 men 60 days to complete a building work.
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{{{RATE*TIME=WORK}}}

{{{20*r*60=1}}}, assuming 1 full piece of work

{{{highlight_green(1200r=1)}}}


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how many days longer would it take 15 men, 
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(Also notice how 15 relates to 20.)


{{{highlight_green(15r*(60+d)=1)}}}


Ratio of the the two equations will eliminate r.

{{{(15r(60+d))/(1200r)=1/1}}}

{{{(60+d)/80=1}}}

{{{d+60=80}}}

{{{highlight(d=20)}}}-------------------twenty more days</PRE>