PSAT Math Multiple-Choice Question 321: Answer and Explanation

Question: 321

Sandy works at a tire store. She gets paid $70 for a day's work, plus a commission of $14 for each tire she sells. Which of the following equations represents the relationship between one day of Sandy's pay, y, and the number of tires she sells, x ?

• A. x = 14y + 70
• B. x = 70y + 14
• C. y = 14x + 70
• D. y = 70x + 14

Correct Answer: C

Explanation:

C

Difficulty: Easy

Category: Word Problems

Getting to the Answer: When writing a linear equation, a flat rate is a constant while a unit rate is always multiplied by the independent variable. For one day of work, Sandy is paid $70, which is a flat rate and should be the constant in the equation. You can identify the unit rate by looking for words like per or for each. The clue "for each" tells you to multiply $14 by the number of tires she sells, so the equation is pay = 14 × number of tires + 70, or y = 14x + 70. This matches (C).