RRB NTPC 28 April 2016 Paper

(3) Days taken by 7 men and 3 women to complete the work = 10 days
Days taken by 8 men and 2 women = 8 days
Let the total work = LCM (10, 8) = 40
Work completed by 7 men and 3 women in 1 day = $\frac{40}{10}$ = 4 units
Work completed by 8 men and 2 women in 1 day $\frac{40}{8}$ = 5 units
Hence, a man completes $\frac{7}{10}$ units of work in 1 day.
∴ Work completed by 12 men
$=\frac{12\times 7}{10}=\frac{84}{10}$ units$\%$ of work done
$=\frac{84}{10\times 40}\times 100=21\%$