3 . In an examination, a student's average marks were 63. If he had obtained 20 more marks in Geography and 2 more marks in history, then his average would have been 65. How many subjects were there in the examination?
4 . A booster pump can be used for filling as well as emptying a tank. The capacity of the tank is 2400 $m^3 $. The emptying capacity of the tank is 10 $m^ 3$ /min higher than its filling capacity and the pump needs 8 minutes lesser to empty the tank than it needs to fill it. What is the filling capacity of the pump?
5 . A and B walking around a circular park at a speed of 2 rounds per hour and 3 rounds per hour respectively. If they start at 8 a.m. from the same point in opposite directions, then how many times shall they meet each other before 9.30 a.m.?
7 . As per the observations of a person, standing exactly midway between two towers, the top of the two towers are at ang1le of elevation of 22.5° and 67.5°. What is the ratio of the height of the taller tower to the height of the shorter tower?