Q: Harry is a professional dog-walker. He is paid to go on long walks with dogs while their families are away from home. On Monday, Wednesday, and Friday, Harry walks 7 dogs. On Tuesday, he walks 12 dogs. And on Thursday he walks 9 dogs. He is paid $5 for each dog that he walks. How many dollars does Harry earn in a week?
A: Monday, Wednesday, and Friday, Harry walks a total of 3 * 7 = 21 dogs. Thus, in a week he walks 21 + 12 + 9 = 42 dogs. At a rate of $5 per dog, Harry ears $5 * 42 = $210 per week. The answer is 210.

Q: Jed is 10 years older than Matt. In 10 years, Jed will be 25 years old. What is the sum of their present ages?
A: Jed is 25 - 10 = 15 years old now. So, Matt is 15 - 10 = 5 years old now. Thus, the sum of their present ages is 15 + 5 = 20. The answer is 20.

Q: Hasan is packing up his apartment because he’s moving across the country for a new job. He needs to ship several boxes to his new home. The movers have asked that Hasan avoid putting more than a certain weight in pounds in any cardboard box. The moving company has helpfully provided Hasan with a digital scale that will alert him if a package is too heavy. Hasan is in the kitchen, and he fills a cardboard box with 38 dinner plates. When he checks the box, the scale reports his box is too heavy. Hasan knows each of his plates weighs 10 ounces. He removes a single plate from the box and checks the movers’ scale again. The scale reports his box is still too heavy. Hasan repeats the process again and again. When he has removed enough plates, the movers’ scale shows the box is now an acceptable weight for shipping. Hasan deduces that each shipping box can hold 20 pounds before the scale says the box is too heavy. How many plates did Hasan need to remove from the shipping box?
A:
Let x be the number of plates removed from the box. Hasan figured out the movers' weight limit was 20 pounds. Since a pound is equal to 16 ounces, each box can hold 20 * 16, or 320 ounces. Each plate weighs 10 ounces, so the weight of the plates in the box after Hasan removes enough plates to satisfy the movers' weight limit is (38 - x) * 10 ounces. Since these two values are equal, we can write the equation (38 - x) * 10 = 320. Dividing both sides by 10 leaves 38 - x = 32. Adding x to both sides gives 38 – x + x = 32 + x, or, 38 = 32 + x. Subtracting 32 from both sides gives the value of x, which is the number of plates removed from the box, 38 - 32 = 32 + x – 32, or, 6 = x. The answer is 6.