Erin runs her own launderette and needs to cash in the change from the machines. There are 80 quarters and 100 dimes in every machine in the launderette. When Erin empties all of the machines and cashes in the change, she has a total of $90. She had no money before she emptied the machines and each machine held the same amount of money. How many machines are in the launderette? Give the rationale and then the answer.
Let's think step by step. There are 4 quarters in a dollar so in quarters, each machine holds 80 quarters / 4 = $20. There are 10 dimes in a dollar so in dimes, each machine holds 100 dimes / 10 = $10. Each machine therefore holds $20 in quarters + $10 in dimes = $30. So Erin must therefore have $90 total income / $30 income per machine = 3 machines.. The answer is: 3.

Tilly counts 120 stars to the east of her house and six times that number to the west. How many stars does she count total? Give the rationale and then the answer.
Let's think step by step. First find the total number of stars she saw in the west: 120 stars * 6 = 720 stars. Then add the number she saw in the east to find the total number: 720 stars + 120 stars = 840 stars.. The answer is: 840.

Mia has 4 times as many shells as David. Ava has 20 more shells than Mia. Alice has half the number of shells Ava has. If David has 15 shells, what the total number of conch shells they all have? Give the rationale and then the answer.
Let's think step by step. If David has 15 shells, then Mia has 4 * 15 = 60 shells. Ava has 20 more shells than Mia, so that is 60 + 20 = 80 shells. Alice has 1 / 2 the number of shells Ava has, which is 1 / 2 * 80 = 40 shells. The total number of shells all of them have is 15 + 60 + 80 + 40 = 195 shells.. The answer is: 195.