Question: In ten years, I'll be twice my brother's age. The sum of our ages will then be 45 years old. How old am I now?
Answer: Let X be my age now. In ten years, I'll be X + 10 years old. In ten years, my brother will be (X + 10) * 1 / 2 years old. In ten years, (X + 10) + (X + 10) * 1 / 2 = 45. So (X + 10) * 3 / 2 = 45. X + 10 = 45 * 2 / 3 = 30. X = 30 - 10 = 20 years old. The answer is 20.

Question: Anthony keeps a bottle of vinegar in his cupboard for 2 years. Each year 20% of the vinegar evaporates. What percent of the vinegar is left after 2 years?
Answer: First find what percent of the vinegar is still in the bottle after each year: 100% - 20% = 80%. Then multiply the amount of vinegar left after one year by the percentage left after each year to find how much is left after 2 years: 80% * 80% = 64%. The answer is 64.

Question: The school is hosting a race after school. The winner is the person who runs the most laps around the school in 12 minutes. One lap around the school is 100 meters. The winner is awarded a gift certificate equal to $3.5 for every one hundred meters they run. The winner runs 24 laps around the school. On average, how much did they earn per minute?
Answer: They ran 2,400 meters because 24 laps x 100 m / lap = 2400 m. They ran 200 meters per minute because 2400 m / 12 min = 200 m / min. For every minute they ran they earned an average of $7 because $3.5 / 100m x 200 m / min = $7 / min. The answer is 7.

Question: Oranges have 80 calories and cost $1.20 each. If Timmy has $10 and needs to make sure he gets 400 calories, how much money will he have left after he buys the oranges he needs?
Answer:
He needs to buy 5 oranges because 400 / 80 = 5. These will cost $6 because 5 x 1.2 = 6. He will have $4 left because 10 - 6 = 4. The answer is 4.