Sarah buys 20 pencils on Monday. Then she buys 18 more pencils on Tuesday. On Wednesday she buys triple the number of pencils she did on Tuesday. How many pencils does she have? Give the rationale and then the answer.
Let's think step by step. By adding together Monday and Tuesday, Saah has 20 + 18 = 38 pencils. On Wednesday, she buys 3 * 18 = 54 pencils. All together, Sarah has 38 + 54 = 92 pencils.. The answer is: 92.

There are five times as many swordfish as pufferfish in an aquarium exhibit. If there are 90 fish total, how many pufferfish are there? Give the rationale and then the answer.
Let's think step by step. Let s be the number of swordfish and p be the number of pufferfish. We know that s = 5p and s + p = 90. Substituting the first equation into the second equation, we get 5p + p = 90. Combining like terms, we get 6p = 90. Dividing both sides by 6, we get p = 15.. The answer is: 15.

Simon and Peter have a big stamp collection. Simon collects red stamps and Peter collects white stamps. Simon has 30 red stamps and Peter has 80 white stamps. If the red stamps are then sold for 50 cents each and the white stamps are sold for 20 cents each, what is the difference in the amount of money they make in dollars? Give the rationale and then the answer.
Let's think step by step. Red stamps are 50 cents each and for 30 stamps, Simon would get 50 * 30 = 1500 cents. White stamps are 20 cents each and for 80 stamps, Peter would get 20 * 80 = 1600 cents. The difference in cents is 1600 - 1500 = 100 cents. One dollar equals 100 cents, so the difference in dollars is 100 / 100 = $1.. The answer is: 1.