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?
Let's think: 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.

John is trying to save money by buying cheap calorie-dense food. He can buy 10 burritos for $6 that have 120 calories each. He could also buy 5 burgers that are 400 calories each for $8. How many more calories per dollar does he get from the burgers?
Let's think: The burritos have 10 * 120 = 1200 calories. That means he gets 1200 / 6 = 200 calories per dollar. The burgers get 5 * 400 = 2000 calories. So he gets 2000 / 8 = 250 calories per dollar. So he gets 250 - 200 = 50 more calories per dollar from the burgers.. The answer is: 50.

Barbeck has two times as many guitars as Steve, but Davey has three times as many guitars as Barbeck. If there are 27 guitars altogether, how many guitars does Davey have?
Let's think: Let x = the number of guitars Steve has. Barbeck has 2x guitars, and Davey has 3 * 2x = 6x guitars. 2x + 6x + x = 27. 9x = 27. x = 27 / 9 = 3 so Steve has 3 guitars. Barbeck has 2 * 3 = 6 guitars. And Davey has 3 * 6 = 18 guitars.. The answer is: 18.

Brady will make $450 more in a year than Dwayne. If Dwayne makes $1,500 in a year, how much will Brady and Dwayne make combined in a year?
Let's think:
Brady will make $450 + $1500 = $1950. Combined, Brady and Dwayne will make $1950 + $1500 = $3450 in a year.. The answer is: 3450.