Joanna has $8. Joanna's brother has thrice as much as Joanna, so he has $8 * 3 = $24. Her sister has half as much as Joanna, then she has $8 / 2 = $4. Together they have $8 + $24 + $4 = $36 altogether.
The answer: 36
Reverse engineering the question: Joanna has $8. Compared to her money, her brother has thrice as much while her sister has only half as much. How much money do the three of them have altogether?

Being women half of the guests, there were 50 / 2 = 25 women in the movie screening. Adding the 15 men to the number of women guests, there were 25 + 15 = 40 men and women. From a total of 50 guests, 50 - 40 = 10 were children. Knowing 1 / 5 of the men left, 15 / 5 = 3 men left. Thus, 3 men + 4 children = 7 people left in all. Therefore, 50 - 7 = 43 people stayed.
The answer: 43
Reverse engineering the question: There were a total of 50 guests in a movie screening of which half of the guests are women, 15 are men, and the rest are children. In the middle of the movie, 1/5 of the men and 4 children left. How many people stayed?

Sandra had 2 bags that each contained 6 pieces of candy so 2 * 6 = 12 pieces. Roger had 11 pieces of candy in one bag and 3 pieces in the other so 11 + 3 = 14 pieces. Roger had 14 pieces and Sandra had 12 pieces so Roger has 14 - 12 = 2 more pieces of candy.
The answer: 2
Reverse engineering the question: Sandra had 2 different bags of candy. Each of her bags had 6 pieces of candy left. Her brother, Roger, also had 2 bags of candy. One of his bags of candy had 11 pieces left and the other had 3 pieces left. How much more candy did Roger have?

He had 40 - 16 = 24 left after using some. Then after giving some away he is left with 24 / 2 = 12.
The answer: 12
Reverse engineering the question:
John buys a box of 40 light bulbs. He uses 16 of them and then gives half of what is left to a friend. How many does he have left?