First find the total difference in weight between the two people: 60 pounds - 40 pounds = 20 pounds. Then divide the weight difference by the weight of each rock to find the number of rocks need to even the weights: 20 pounds / 4 pound / rock = 5 rocks.
The answer: 5
Reverse engineering the question: Jack, who weighs 60 pounds, wants to play on the see-saw with his cousin Anna, who weighs 40 pounds. How many 4-pound rocks does Jack need to hold to make their weights equal?

Sally takes 24 + 2 = 26 seconds. Diane takes 24 - 3 = 21 seconds. Thus, the three take 24 + 26 + 21 = 71 seconds to run the 600 - meter relay race.
The answer: 71
Reverse engineering the question: Rhonda, Sally, and Diane are members of their school's track team. The three of them run the 600-meter relay race together. Rhonda runs the first 200 meters of the race, Sally runs the second 200 meters of the race, and Diane runs the final 200 meters of the race. Rhonda can run 200 meters in 24 seconds. Sally takes two seconds longer to run the same distance, while Diane can run 200 meters three seconds faster than Rhonda. How many seconds does it take for the three of them to run the 600-meter relay race?

On Tuesday, Adam bought 3 * 15 apples = 45 apples. On Wednesday, Adam bought 4 * 45 apples = 180 apples. Adam bought 15 apples + 45 apples + 180 apples = 240 apples on the three days.
The answer: 240
Reverse engineering the question: Adam bought 15 apples on Monday. On Tuesday he bought 3 times that quantity. On Wednesday he bought 4 times the quantity he bought on Tuesday. What is the total quantity Adam bought on these three days?

Camden went swimming 16 / 4 = 4 times a week. Susannah went swimming 24 / 4 = 6 times a week. Susannah went 6 - 4 = 2 more times a week than Camden.
The answer: 2
Reverse engineering the question:
Camden went swimming 16 times in March and Susannah went 24 times. If the number of times they went throughout the month was divided equally among 4 weeks, how many more times a week did Susannah swim than Camden?