75) A man covers half of his journey at 6 km/ hr and the remaining half at 3 km/ hr. His average speed is

76) The average weight of 8 boys is increased by 1.5 kg when one of the boys, who weights 65 kg, is replaced by a new boy. The weight of the new boy is

77) The ratio between the present ages of Ravi and Jai is 3:2. If Ravi was 6 years older than Jai, four years back, how old is Jai now?

78) By selling a tape-recorder for 950, I lose 5%. What percent shall I gain by selling it for a 1040?

79) When 1 is added to each of the given two numbers, their ratio becomes 3 : 4 and when 5 is subtracted from each, the ratio becomes 7 : 10. The numbers are