30 workers can complete a job in 20 days. After how many days should 9 workers leave the job so that the work is completed in total 26 days:
A) 12
B) 10
C) 6
D) None of these

• C) 6
  
  30 worker's 1 day work=1/20 and
  21 worker's 1 day work=21/(30*20)=7/200
  If 9 workers leaves after 'x' days, then 30 workers works for 'x' days, so 30-9=21 worker will work for 26-x days to complete the work.
  So (x/20) + (26-x)*7/200= 1
  x=6
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• we can solve this ques also through options.
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