Question 984653
Focus on hours, and attempt to find the one-man rate.


{{{30r*(8*10)=120}}}, the 8*10 being the number of hours.
{{{r=120/(30*80)=12/240=6/120=1/20}}}, the one man rate, articles per hour.


Next, you will have the sum of two terms.


30 men for 4 days at 10 hours per day, and then  20 men for t unknown rate in hours per days .  Still at 8 hours per day.  Sum must still be 120 articles.
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{{{30(1/20)*(4*10)+20(1/20)*(4*t)=120}}}


Find t, the hours per day that those 20 remaining men must work.