Marcus had 18 / 2 = 9 pebbles left. After Freddy gave him more, he has 9 + 30 = 39 pebbles.
The answer: 39
Reverse engineering the question: Marcus had 18 pebbles. He skipped half of them across the lake, but Freddy gave him another 30 pebbles. How many pebbles does Marcus have now?

There are 9 + 12 = 21 students in a class. Hence, 21 / 3 = 7 groups are formed.
The answer: 7
Reverse engineering the question: There are 9 boys and 12 girls in a class. The teacher needs to create groups with three members for their class activity. How many groups are formed?

Half of the trip lasts for 8 * 0.5 = 4 hours. During the first half, Martin did 4 * 70 = 280 kilometers. And during the second half 4 * 85 = 340 kilometers. In total Martin traveled 280 + 340 = 620 kilometers during his business trip.
The answer: 620
Reverse engineering the question: Martin went on an eight-hour business trip. During the first half of the trip, he traveled at a speed of 70 kilometers per hour and during the second half at a speed of 85 kilometers per hour. How many kilometers did he travel during the journey?

The blue weights weigh 4 * 2 = 8 pounds. The green weights weigh 5 * 3 = 15 pounds. The weights weigh 8 + 15 = 23 pounds. The total is then 23 + 2 = 25.
The answer: 25
Reverse engineering the question:
At a gym, the blue weights are 2 pounds each, and the green weights are 3 pounds each. Harry put 4 blue weights and 5 green weights onto a metal bar. The bar itself weighs 2 pounds. What is the total amount of weight, in pounds, of Harry's custom creation?