Question

Neil reads equal numbers of pages of a book every week. The graph shows the number of pages of the book left to read, y, after x weeks: A graph titled Neil’s Book Reading shows Number of Weeks on the x-axis and Number of Pages Left on the y-axis. The scale on the x-axis shows numbers from 0 to 5 at increments of 1, and the scale on the y-axis shows numbers from 0 to 315 at increments of 45. A straight line joins the ordered pairs 0, 225 and 1, 180 and 2, 135 and 3, 90 and 4, 45 and 5, 0. Which equation best models the relationship between x and y?

y = −5x + 45
y = −45x + 315
y = −5x + 225
y = −45x + 225

Answer 1

Explanation:

For every increment of 1 across the x-axis,

the line decreases by 45 units.

Hence the slope is

Rise / Run = (-45)/1 = -45.

The point (0, 225) tells us that the

y-intercept is 225.

y = mx + c, where m is the line's slope and c is the y-intercept.

Hence we have y = -45x + 225.