3. In a certain city, the number of commuters decreased 15 per cent from June to July and decreased 10 per cent from July to August. By approximately what per cent would the number of commuters have to increase from August to September for the number of commuters in September to be equal to the number of commuters in June?
4. If the distance required for an automobile to stop varies directly as the square of its speed, what is the distance required for an automobile driven at 60 km/hr to stop if it takes 10 meters to stop the automobile moving at 20 km/hr.
5. Technological advances in manufacturing radios reduced the manufacturing cost of parts by 50 per cent and the cost of labour by 60 per cent. If labour originally accounted for 3 times as much of the manufacturing cost as parts and it is assumed that total cost consisted only of labour and parts, what was the per cent decrease in the total cost, resulting from these advances?
9. X can clean the garage in half the time it takes B. If they cleaned it together in 3 hours, how many hours would it take form X to clean the garage all by himself?