Arun invested a sum of money at a certain rate of simple interest for a period of four years. Had he invested the same sum for a period of six years, the total interest earned by him would have been fifty percent more than the earlier interest amount. What was the rate of interest percent per annum?
The ratio of the age of a father and a son at present is 5: 2. Four years hence the ratio of the ages of the son and his mother will be 1 : 2. What is the ratio of the present ages of the father and the mother?