The number of blue apples is 5, and if you receive twice as many yellow apples as the number of blue apples, there will be 5 * 2 = 10 yellow apples. After receiving the yellow apples, you now have 10 yellow apples + 5 blue apples = 15 apples. When you give 1 / 5 of the total number of apples to the son, you part with 1 / 5 * 15 = 3 apples. The total number of apples remaining is 15 - 3 = 12 apples.
The answer: 12
Reverse engineering the question: I have purchased 5 blue apples at the store. Suppose my neighbor gives me twice as many yellow apples as I have blue ones, and then I give my son 1/5 of the total number of apples; how many apples do I have now?

If X = "Price of Reuben" We know that 10(X) + 5(X + 2) = 55. Therefore 10X + 5X + 10 = 55. Therefore 15X = 45. Therefore, the price of a Reuben is $3 because 45 / 15 = 3. The price of pastrami is $5 because 3 + 2 = 5.
The answer: 5
Reverse engineering the question: Reuben opens a sandwich shop selling his namesake sandwich and pastrami sandwiches. Pastrami cost $2 more than the Reuben. He sells 10 Reubens and 5 Pastrami sandwiches and earns $55. How much does a pastrami sandwich cost?

First find how many ounces of carbon dioxide are released per shopping trip: 8 bags / trip * 4 oz / bag = 32 oz / trip. Then divide that amount by the number of ounces per pound to find the pounds of carbon per shopping trip: 32 oz / trip / 16 oz / pound = 2 pounds / trip. Then divide the amount of carbon used to make the tote bag by the amount of carbon saved per shopping trip to find the number of trips needed for the bag to be a better option: 600 pounds / 2 pounds / trip = 300 trips.
The answer: 300
Reverse engineering the question: Marla is thinking about getting a canvas tote bag to avoid using plastic bags at the grocery store. If making the canvas bag released 600 pounds of carbon dioxide, each plastic bag released 4 ounces of carbon dioxide, and Marla uses eight bags per shopping trips, how many shopping trips will she have to make before the canvas bag is the lower-carbon solution? (There are 16 ounces in a pound.)

Joey Chestnut ate 75 hotdogs to claim the record and Lisa has eaten 20 hot dogs so far, so she still needs to eat 75 - 20 = 55 hotdogs to tie Joey Chestnut. Lisa has a 10 minute time period to eat the hotdogs and half the time has already passed, which means Lisa has 10 / 2 = 5 minutes left until the competition is over. If she needs to eat 55 hotdogs to tie Joey Chestnut and there are 5 minutes left in the competition period then she needs to eat 55 / 5 = 11 hot dogs per minute to have a chance of tying for a win.
The answer: 11
Reverse engineering the question:
Lisa is looking to attempt a World Record. She has decided to try and match Joey Chestnut's record of eating 75 full hotdogs, buns included, in 10 minutes. Halfway through the time Lisa has eaten 20 hotdogs. How many hotdogs will she have to eat per minute to at least tie Joey Chestnut's record?