PSAT Math Multiple-Choice Question 314: Answer and Explanation

Question: 314

Months after June	4	8	10
Price of Gas	2	3.33	4

In June, Marie notices that the price of gas is increasing. She records the price of gas 4, 8, and 10 months after her initial observation. If y is the price of gas, in dollars per gallon, and x is the number of months after June, which linear equation represents the correct relationship between y and x ?

• A. y = 0.33x + 0.67
• B. y = 0.67x + 1.33
• C. y = 1.33x + 2
• D. y = 2.67x + 5.67

Correct Answer: A

Explanation:

A

Difficulty: Medium

Getting to the Answer: The question tells you that the relationship is linear, so start by finding the the slope, m, using any two pairs of values from the table and the slope formula. Next, substitute the slope and any pair of values from the table, such as (4, 2) and (10, 4), into the equation y = mx+b and solve for b. Finally, use the values of m and b to write the function:

You can stop right there! Only (A) has a slope of 0.33, so it must be the correct answer. For the record: