Question

Marcus has his car insurance payment directly withdrawn from his savings account. One month after starting the payment, he had $915 in savings. Nine months after starting the payment, he had $235. Assume Marcus made no other deposits or withdrawals from the account. If the relationship between months and the amount of money in Marcus’s account is linear, what is the slope?

Answer 1

The slope of a line is given that passes through the points (x1,y1) and (x2,y2) is given by:

$m=\frac{y_2-y_1}{x_2-x_1}$

In this case we know that:

After one month the account has $915, this can be represented by the point (1,915)

After nine months the account has $235, this can be represented by the point (9,235).

Plugging these two points in the expression for the slope we have:

$\begin{gathered} m=\frac{235-915}{9-1} \\ m=\frac{-680}{8} \\ m=-85 \end{gathered}$

Therefore, the slope is -85.