If 3 men or 4 women can build a wall in 43 days, in how many days can 7 men and 5 women build this wall ?

Explanation:

3 men = 4 women

1 man = (4/3) women ,

7 men + 5 women = (7×4\3+5)=43\3 women

M1 =4, D1 = 43, M2 = 43/2, D2 =?

and W1 = W2 = 1

According to the formula,

M1D1W2 = M2D2W1

4 x43x1=(43/3)xD2 x1

D2 = 3 x 4 = 12 days