4 . With a given rate of simple Interest, the ratio of Principal and Amount for a certain period of time is 4:5 After six years, with the same rate of interest, the ratio of the Pricipal and Amount becomes 5:7 The rate of interest is ?
7 . Three men A,B and C working together can do a job in 6 hours less time than A alone, in 1 hour less time than B alone and in one half the time needed by C when working alone. Then A can do the complete job in ?
8 . 150 workers were engaged to finish a piece of work in certain number of days. Four workers dropped the second day, four workers dropped the third day and so on. It takes 8 more days to finish the work now. Find the number of days in which the work was completed ?
10 . Two cars start together in the same direction from the same place. The first goes with uniform speed of 10 km/hr. The second does at a speed of 8 km/hr in the first hour and increases the speed by $1\over 2$ km in each succeeding hour. After how many hours will the second overtake the first car if both cars go non - stop ?