PSAT Math Multiple-Choice Question 68: Answer and Explanation

Question: 68

Between 2010 and 2015, researchers tracked populations of Crucian carp in the Ohio River. The graph above displays population sizes as counted by the researchers. According to the line of best fit, what is the approximate average yearly decrease in the number of Crucian carp?

• A. 1
• B. 2.5
• C. 1,200
• D. 2,500

Correct Answer: D

Explanation:

D

The question asks for approximate average yearly decrease in the number of Crucian carp based on the line of best fit shown in the graph. In this graph, the slope of the line of best fit represents the average yearly change. To formula for slope is . Choose two points from the graph to plug into the slope formula. On the graph, the number of carp in 2010 was 25,000 and in 2011, the number of carp was 22,500. Using these x- and y-values, the expression becomes . Simplify the expression to get , or -2,500. Since the result is negative, it represents a decrease of 2,500 carp per year. The correct answer is (D).