Ans: Given, work can be done by:
3*20 = 60 man-days
or
6*20 = 120 boy-days
therefore
60 md = 120 b.d

divide by 60
md = 2bd
:
how many days will 6 men and 8 boys take to do the same work?
let d = no. days to accomplish this in terms of man-days
we know that 8bd = 4 md; therefore
6d + 4d = 60
10d = 60
d = 6 days for 6 men and 8 boys to do the job

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