50. If 3 men or 6 boys can do a piece of work in 10 days working 7 hours .a day how many days will a ta
A.6
B.7
C.8
D.9
51. 2 men and 7 boys can do a piece of work in 14 days; 3 men and 8 boys can do the same in 11 days Then
A. 18 days
B. 21 days
C. 24 days
D. 30 days
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