PSAT Math Multiple-Choice Question 311: Answer and Explanation

Question: 311

A produce stand normally sells watermelons for $0.60 per pound. On Mondays, it sells watermelons at a 20 percent discount. The stand also sells sweet potatoes for $0.79 each. Which of the following represents the total cost, c, if a customer buys 4 sweet potatoes and a watermelon weighing p pounds on a Monday?

• A. c = 0.2p + 0.79
• B. c = 0.48p + 3.16
• C. c = 0.6p + 0.79
• D. c = 0.6p + 3.16

Correct Answer: B

Explanation:

B

Difficulty: Medium

Getting to the Answer: Write the equation in words first, then translate from English to math. The total cost, c, is the weight of the watermelon in pounds, p, multiplied by the sale price. Since the purchase is made on Monday, the sale price is: $0.60 × 80% = 0.6 × 0.8 = 0.48. This gives the cost of the watermelons: 0.48p. Now, add the cost of four sweet potatoes, 0.79 × 4 = 3.16, to get the equation c = 0.48p + 3.16, which matches (B).

You could also use the Picking Numbers strategy: pick a number for the weight of the watermelon and calculate how much it would cost (on sale). Next, add the cost of four sweet potatoes. Finally, find the equation that gives the same amount.