Teddy has 7 + 8 = 15 pets in total. Ben has 9 + 7 = 16 dogs, which means he has 16 pets in total. Dave has 13 + 8 = 21 cats. Dave has 7 - 5 = 2 dogs. Dave has 21 + 2 = 23 pets in total. Combined, they have 15 + 16 + 23 = 54 pets in total.
The answer: 54
Reverse engineering the question: Teddy has 7 dogs and 8 cats. Ben has 9 more dogs than Teddy, and Dave has 13 more cats and 5 less dogs than Teddy. How many pets do all of them have combined?

If the price of a lawnmower was $1800 a year ago, 2 / 5 less than the cost right now, then it now costs 2 / 5 * 1800 = $720 more to buy one lawnmower. The total cost of buying one lawnmower right now is $1800 + $720 = $2520. To purchase 4 such lawnmowers, Mr. Lucian will have to pay $2520 * 4 = $10080.
The answer: 10080
Reverse engineering the question: A year ago, the total cost of buying a lawnmower was 2/5 times less than the cost it goes for now. If the cost was $1800 a year ago, calculate how much it would cost Mr. Lucian to buy 4 such lawnmowers.

The total ratio of the coins they both have is 10 + 45 = 55. The fraction of the ratio representing the number of coins that Amalie has is 45 / 55, and since the total number of coins they both have is 440, Amalie has 45 / 55 * 440 = 360 coins. When Amalie spends 3 / 4 of what she has, she parts with 3 / 4 * 360 = 270 coins. She still has 360 coins - 270 coins = 90 coins.
The answer: 90
Reverse engineering the question: The ratio of coins that Elsa has to that which Amalie has is 10:45. If the total number of coins they have is 440, and Amalie spends 3/4 of what she has on toys, how many will she remain with?

Angie earned 80 and paid 42 for necessities, so she had 80 - 42 = $38 left. Angie had 18 left after paying taxes, so her share of the taxes was 38 - 18 = $20 this month.
The answer: 20
Reverse engineering the question:
Angie is part of a household with shared expenses and contributes $42 a month for necessities. She has a salary of $80 per month. She also pays a share of the household taxes each month. At the end of this month, she had $18 left over. How much did she pay in taxes this month?