[Question]Out of the 80 students who took the biology exam, only 2/5 of them managed to score 100%. If a score below 80% qualified as failing, and 50 percent of the remaining students who didn't score 100% managed to score over 80%, calculate the number of students who failed the exam.
[Answer]The number of students who scored 100% is 2 / 5 * 80 = 32. Out of the 80 students, 80 - 32 = 48 did not score 100%. If 50% of the students who did not score 100% managed to score over 80%, then 50 / 100 * 48 = 24 students scored over 80%. The number of students who failed is 48 - 24 = 24. The answer is 24.

[Question]There are 6 forks in the cutlery drawer. There are 9 more knives than forks, and there are twice as many spoons as knives and half as many teaspoons as forks. After 2 of each cutlery is added to the drawer, how many pieces of cutlery are there in all?
[Answer]There are 6 + 9 = 15 knives. There are 15 x 2 = 30 spoons. There are 6 / 2 = 3 teaspoons. There are 6 + 15 + 30 + 3 = 54 pieces before adding more cutlery. 2 of each 4 types of cutlery are added, and therefore 2 x 4 = 8 pieces added. In total there are 54 + 8 = 62 pieces of cutlery in the drawer. The answer is 62.

[Question]A swimming pool is being emptied through a drain at the bottom of the pool and filled by a hose at the top. The drain can empty the pool in 4 hours and the hose can fill the pool in 6 hours. The pool holds 120 liters of water. If the pool starts filled with water, how much water will be left after 3 hours?
[Answer]It takes the drain 4 hours to empty the pool, so it drains at a rate of 120 liters / 4 hours = 30 liters / hour. After 3 hours, the drain will have removed 3 * 30 = 90 liters of water from the pool. It takes the hose 6 hours to fill the pool, so it fills at a rate of 120 liters / 6 hours = 20 liters / hour. After 3 hours, the hose will have added 3 * 20 = 60 liters of water to the pool. After 3 hours, there will be 120 liters + 60 liters – 90 liters = 90 liters of water left in the pool. The answer is 90.

[Question]Yulia was able to net $44 in profit this week. Her lemonade stand made a gross revenue of $47 this week. She was also able to babysit and made $31. However, her lemonade stand is expensive to run because she needs to buy lemons, sugar, and sunscreen. How much did she spend to operate her lemonade stand, in dollars?
[Answer]
Yulia's total gross revenue was $47 + $31 = $78. To calculate her overhead we must subtract her total profit from her gross revenue which is $78 - $44 = $34. The answer is 34.