### Home > AC > Chapter 4 > Lesson 4.2.2 > Problem4-80

4-80.

It's the end of the semester, and the clubs at school are recording their profits. The Science Club started out with $20$ and has increased its balance by an average of $10$ per week. The Math Club saved $5$ per week and started out with $50$ at the beginning of the semester. 4-80 HW eTool (Desmos).

1. Create an equation for each club. Let $x$ represent the number of weeks and $y$ represent the balance of the club's account.

2. Graph both lines on one set of axes. When do the clubs have the same balance?

3. What is the balance at that point?

What is the Science Club's starting point?
($y$-intercept or $b$)

How much does their balance increase every week?
(growth rate or $m$)

Put this into equation $\left(y = mx + b\right)$ format.

Follow the same steps to find an equation for the Math Club.

What are the $x$- and $y$-values of the point where the two lines intersect?

Complete the tables in the eTool below to help you with this problem.
Click on the link at right for the full eTool version: AC 4-80 HW eTool