The 5th graders planted 30 x 2 = 60 trees. Thrice the number of trees planted by the 5th graders is 60 x 3 = 180. So, the 6th graders planted 180 - 30 = 150 trees. Therefore, they planted a total of 30 + 60 + 150 = 240 trees.
The answer: 240
Reverse engineering the question: A school does a yearly tree planting activity. This year, the 4th graders planted a total of 30 trees while 5th graders planted twice as many. The 6th graders planted 30 fewer than thrice the number of trees planted by the 5th graders. How many trees did they plant altogether?

The cat received half as many fish as the number given to the dog, which means the cat received 1 / 2 * 40 = 20 fish. This means Keanu bought 20 + 40 = 60 fish at the store. If each fish cost him $4, the total cost for the fish he bought at the store is 60 * $4 = $240.
The answer: 240
Reverse engineering the question: Keanu bought some fish from the store for his pets. He gave his cat half as many fish as he gave to his dog. If he gave his dog 40 fish, and each fish cost him $4, calculate the total amount of money he spent at the store to buy all the fish.

If a third of the cats have spots and a quarter of those are fluffy (1 / 3) x (1 / 4) = 1 / 12 cats are both fluffy and spotted. Out of 120 cats, 120 cats / 12 = 10 cats are spotted and fluffy.
The answer: 10
Reverse engineering the question: A third of all the cats in the village have spots. A quarter of the spotted cats in the village are fluffy. If there are 120 cats in the village, how many of the cats are spotted and fluffy?

John earnt $18 / 2 = $9 on Sunday. In total, John made $18 + $9 + $20 = $47 over the two weekends. John needs $60 - $47 = $13 extra to buy the pogo stick.
The answer: 13
Reverse engineering the question:
John earned $18 on Saturday but he only managed to earn half that amount on Sunday. He earned $20 the previous weekend. How much more money does he need to earn to give him the $60 he needs to buy a new pogo stick?