Question: Cathy and Chris got summer jobs at the cake shop and were supposed to work 20 hours per week each for 2 months. During that time, Chris got sick for one week and Cathy took her shifts. If there are four weeks in a month, how many hours did Cathy work during the 2 months?
Answer: There are 4 weeks in a month so Cathy and Chris were supposed to work for 4 weeks / month x 2 months = 8 weeks each. Since Chris got sick then Chris was only able to work for 8 weeks - 1 week = 7 weeks while Cathy worked for 8 weeks + 1 week = 9 weeks. Therefore, Cathy worked for 9 weeks x 20 hours / week = 180 hours. The answer is 180.

Question: 4 students participated in a 200m race. If the average completion time of the last three students was 35 seconds, and the average completion time of all four runners was 30 seconds, how long (in seconds) did it take the student who came first to finish the race?
Answer: The last 3 students had an average completion time of 35 seconds so the sum of their completion times was 3 * 35 = 105 seconds. All 4 students (now including the student who came first) had an average completion time of 30 seconds, meaning the sum of their completion times is 4 * 30 = 120 seconds. The student who came first spent 120 - 105 = 15 seconds in the race. The answer is 15.

Question: Lidia has a collection of books. Her collection is four times bigger than the collection which her friend Susan has. In total Susan and Lidia, both have 3000 books. How many books does Susan have in her collection?
Answer: Let x be the number of books in Susan's collection. The collection of both Susan and Lidia would then be 4 * x + x = 3000. 5 * x = 3000. x = 600. The answer is 600.

Question: Haley grows at the rate of 3 inches every year. If she is currently 20 inches tall, what will be her height after 10 years?
Answer:
After 10 years, growing at the rate of 3 inches every year, Haley will have grown by 3 * 10 = 30 inches. If she is currently 20 inches tall, her height after 10 years will be 20 + 30 = 50 inches. The answer is 50.