A scatterplot’s line of best fit predicts an overall trend, and its slope tells you how the predicted output changes for one more input unit. Pick two readable points on the line, not two data dots, then divide the output change by the input change. Desmos can handle the arithmetic. A line that falls as you move right represents a decrease.
Hints
- Hint 1
The line of best fit shows predicted times; the dots show individual measured times. To find the predicted rate, choose two points you can read on the drawn line, even if neither has a dot. Which two points on the line can you read?
- Hint 2
Slope is the change in the vertical value divided by the change in the horizontal value. Subtract in the same order on top and bottom. The units will tell you what changes for each additional practice session.
Step-by-step
Read two points on the fitted line
Step 1Choose points on the line
The drawn line passes through and : at sessions its predicted time is minutes, and at sessions its predicted time is minutes. The dot near is an observation, an actual measured time, not a point on the line.
- Step 2
Set up the slope with the right units
Slope is the change in predicted time divided by the change in practice sessions. Subtract in the same order for both changes, so the slope is minutes per session, not sessions per minute.
- Step 3
Calculate and interpret the rate
Type into Desmos. It returns . The minus sign means a decrease: for each additional practice session, the line predicts about fewer minutes to solve a puzzle. Choice A.