Q: Phoebe eats 1 serving and gives her dog 1 serving of peanut butter for a bedtime snack. Each jar of peanut butter has 15 servings. How many jars will she need to make sure she and her dog have enough to last for 30 days?
A: She and her dog both have a serving before bed so they eat 1 + 1 = 2 servings a day. She wants to have enough for 30 days and they eat 2 servings a day so they need 30 * 2 = 60 servings. Each jar has 15 servings and she needs 60 servings so she will need 60 / 15 = 4 jars of peanut butter. The answer is 4.

Q: Melony makes $21 of profit every time she sells 3 shirts and four times as much profit when she sells two pairs of sandals. How much profit will she make if she sells 7 shirts and 3 pairs of sandals?
A: Melony makes $21 * 4 = $84 of profit for two pairs of sandals. Melony makes $84 / 2 pairs = $42 of profit per pair of shoes. Melony makes $21 / 3 shirts = $7 of profit per shirt. For seven shirts, Melony will make 7 shirts * $7 = $49 of profit. For three pairs of sandals, Melony will make 3 pairs * $42 / pair = $126 of profit. Melony will make a total of $49 + $126 = $175 of profit. The answer is 175.

Q: There are 50 marbles in a box which has a mixture of white, red and blue marbles. There were originally 20 white marbles and an equal number of red and blue marbles. Jack removes a number of marbles equal to double the difference between the number of white marbles and the number of blue marbles. How many marbles are left in the box?
A:
20 of 50 marbles are white so there are 50 - 20 = 30 red and blue marbles. The number of red marbles and blue marbles is the same, so there are 30 / 2 = 15 of each color. The difference between the number of white marbles and blue marbles is 20 - 15 = 5. Double the difference is 5 * 2 = 10 marbles. 10 marbles are removed to leave 50 - 10 = 40 marbles. The answer is 40.