The scatterplot above shows the number of minor muscle strain injuries sutained in a year by athletes, plotted against their self-reported amount of time spent stretching and doing other "warm up" activities before energing in rigorous physical activity. Which of the following best estimates the average rate of change in the number of injuries compared with the number of minutes spent warmig up ?

Options

A. `-1.2`
B. `-0.8`
C. `2`
D. 20

Answer

A

Explanation

Examine the graph, paying careful attention to units and lables. The average rate of change is the same as the slope of the line of best fit. The data is decreasing (going down from left to right), so eliminate (C ) and (D). To choose between (A) and (B), find the slope of the line of best fit using the slope formula, `m = (y_(2) - y_(1))/(x _(2) -x_(1)),` and any two points that lie on (or very close to) the line. Using the two points `(5,14) and (10,8),` the average rate of change is about `(8-14)/(10-5)=(-6)/(5)=-1.2,` whihc matches (A).