A straight-line graph shows a linear relationship: the output starts at one value and changes by the same amount each minute. Read the vertical-axis crossing for the starting number of pages, then compare two points one minute apart for the rate. Match both the start and the rate; matching only one can lead you to the wrong equation.
Hints
- Hint 1
The vertical intercept is where the line crosses the pages axis. Time is there, so that page count is the starting amount, not the number printed each minute. What does the graph show at ?
- Hint 2
The slope tells you how many pages are added per minute. Compare the page counts at and , which are one minute apart. How much does the count rise?
- Hint 3
In slope-intercept form, , the rate multiplies time, while is the count at time . Put your two graph readings into those different roles.
Step-by-step
Read the start and the one-minute rise
Step 1Find the starting page count
No Desmos needed. Read the starting value and the one-minute rise off the graph. At , the line crosses the pages axis at . This vertical intercept gives the output when time is , so the printer has produced 30 pages when the timer starts.
- Step 2
Find the pages printed per minute
The line passes through and . Those times are one minute apart, so the change in pages over that minute is the slope, or pages printed per minute. Subtract the page counts:
Use the axis labels here: each vertical tick represents pages, not page.
- Step 3
Write the equation
A line has slope-intercept form , where is the pages printed per minute and is the page count at . Use the rate of and the starting count of :
The printer starts at pages and adds each minute. Choice A.