[EX03-074] Interstate 90, the longest of the east–west U.S. interstate highways, is 3112 miles long, stretching from Boston, Massachusetts, at I-93 on the eastern end to Seattle, Washington, at the Kingdome on the western end. It travels across 13 northern states; the number of miles and number of intersections in each of these states are listed below.

State WA ID MT WY SD MN WI No. of Inter. 57 15 83 23 61 52 40 Miles 298 73 558 207 412 275 188 State IL IN OH PA NY MA No. of Inter. 19 21 40 14 48 18 Miles 103 157 244 47 391 159 Source: Rand McNally and http://www.ihoz.com/I90.html

a. Construct a scatter diagram.

b. Find the equation for the line of best fit using x  miles and y  intersections.

c. Using the equation found in part

b, estimate the average number of interchanges per mile along I-90.