At a party there are only single women and married men with their wives. The probability that a randomly selected woman is single is 2/5. What fraction of the people in the room are married men?
Let number of single women be ws and number of married women be wm (Hence number of men = wm)
We are told: ws/wm = 2/5
fraction of men: fm = wm/(ws+2wm)
Divide numerator and denominator by wm: fm = 1/(ws/wm + 2), hence fm = 1/(2/5 + 2) or fm = 5/12