Hi

Let a man's daily work is x units and that of a boy is y units.

So total amount of work, W = 5(12x + 16y) = 4(13x + 24y)

=> 60x + 80y = 52x + 96y

=> 8x = 16y

=> x = 2y i.e. W = 5(24y + 16y) = 200y.

Now 7men and 10 boys' work of a day is = 7x + 10y = 14y + 10y = 24y.

So total days required to finish the work is = 200y/24y = 25/3 = 8 and 1/3 days.

Kamal Lohia