Home > GB8I > Chapter 9 Unit 10 > Lesson INT1: 9.1.3 > Problem9-39

9-39.

A gallon of milk that cost $$3.89$ a year ago now costs$$4.05$.

Remember the independent variable ($x$) represents years, while the dependent variable ($y$) represents price.

There are two points in this problem.
Point $1$: $(-1, 3.89)$ one year ago cost $$3.89$ Point $2$: $(0, 4.05)$ now costs$$4.05$.

1. If the cost is increasing linearly, what is the growth rate? If the cost kept increasing in the same way, what will the milk cost $5$ years from now?

Read the Math Notes box in Lesson 2.3.2 on finding equations of lines with 2 points.

Remember that slope is $\frac{ \Delta y} { \Delta x}$

Growth rate is $$0.16$ per year. The price in $5$ years will be$$4.85$.

1. If the cost is increasing exponentially, what is the growth rate? What will the milk cost in $5$ years?

Review problem 8-121 for a method of solving this problem.

Remember there should be $2$ equations (system of equations) and use the Equal Values Method.

The multiplier is $1.04$ ($4$%). The price in $5$ years will be \$$4.93$.