In a college 7 period a day each of 45 minutes duration. How long each period be, if the school has 9 periods a day assuming the number of hours to be the same?

8 In a toy company, it requires 36 machines to produce a car toys in 54 days. How many machines would be required to produce the same number of car toys in 81 days?  9 Two persons could fit the AC unit in a house in 2 days one person fell ill before the work started, how long would the job take now? 11 There are 200 students in a primary school. They need 50 litres of drinking eater/day. If 50 of them are reduced how many litres of water needed per day? 12 If the weight of 25 precious stones is 50 grams. How many precious stones of the same type would weigh 4500 kilograms.