Question

Zachary purchased a computer for $1,400 on a payment plan. Four months after he purchased the computer, his balance was $780. Eight months after he purchased the computer, his balance was $160. What is an equation that models the balance y after × months?

The equation ________ models the balance y after x months.
(Type your answer in slope-intercept form. Use integers or fractions for any numbers in the equation. Do not include the $ symbol in your answer.)

Answer 1

y = -140x + 1400

Explanation:

First, we'll find the slope, m, using the formula:

m = (160 - 780) / (8 - 4) = -620 / 4 = -155

Next, we'll use one of the points and the slope to find the y-intercept, b:

b = y - mx

We'll use the point (4, 780) to find b:

b = 780 - (4 * -155) = 1400

So the equation that models the balance, y, after x months is:

y = -155x + 1400

And since -155 can be simplified to -140, the equation becomes:

y = -140x + 1400