Tioga Road is a mountain pass that crosses the Sierra nevada through northern Yosemite National Park. The road is closed from about November through late May. This time period can change depending on the quantity and nature of the season's snowfall, as well as unforeseen obstacles such as fallen trees or rocks. The scatterplot above compares the snowpack water content on April 1 (for year 1981-2014) as a percent of the historical average to the time it takes th National Park Service to fully clear the road and open it to traffic.
For every 5 percent increases in snowpack water content, how many more days does it take the National Park Service to clear Tioga Road ?

Answer

2

Explanation

You're asked fro a rate, this means finding the slope of the line of best fit. Start by picking a pair of points, preferbly where the line of best fit passes through a grid line intersection to minimize error. The points (0,0) and (50,20) are good choices to make the calculation easy. Determine the slope:
`m = (y _(2) -y_(1))/(x_(2) -x_(1)) = (20-0)/(50-0)=(20)/(50)=2/5`
Don't grid in `2/5,` though. Remember what you're being asked: you need the road clearing duration increase for a `5%` increase in snowpack water content, not a `1%` increase. Therefore, multiply `2/5` by 5, which yields 2. Grid in 2.