MIA U4D18 Warmup: Matt Follow the order of operations. On a group quiz, your group needs to calculate the answer to 12 – 2 * 6 – 3. The three other group members came up with these answers: Marta: 57 Matt: -3 Miguel: 30 Who, if anyone, is correct? What would you say to the other group members to convince them? Matt Follow the order of operations.

OBJ: Students will: Use the equation of a linear model to make predictions about the data

Buying on Credit: Electric Avenue sells audio/video, computer, and entertainment products. The store offers 0% interest for 12 months on purchases made using an Electric Avenue store credit card.

Buying on Credit: 1. Emily purchases a television for $580 using an electric Avenue store credit card. Suppose she pays the minimum monthly payment of $25 each month for the first 12 months.   a. Complete a table of (number of monthly payments, account balance) values for the first 6 months after the purchase, then plot those values on a graph. $580 $555 $530 $505 $480 $455 $430

b. Will Emily pay off the balance within 12 months? How do you know? c. If you know Emily’s account balance NOW, how can you calculate the NEXT account balance, after a monthly payment? d. Which of the following function rule(s) gives Emily’s account balance E after m monthly payments have been made? E = 25m – 580 E = m – 25 E = -25m + 580 E = 580 + 25m E = 580 - 25m No; Her balance isn’t 0 after 12 payments of $25. It’s $280. Next = Now – 25; Start at 580. E = -25m + 580 or E = 580 – 25m

Buying on Credit: e. Determine the rate of change, including units, in the account balance as the number of monthly payments increases from: 0 to 2; 2 to 3; 3 to 6; i. How does the rate of change reflect the fact that the account balancedecreases as the number of monthly payments increases? ii. How can the rate of change be seen in the graph from Part a? In the function rule(s) you selected in Part c? -$50/2 = -$25/month -$25/1 = -$25/month -$75/3 = -$25/month Negative Slope Balance decreases as number of payments increases -25

Buying on Credit: f. How can the starting account balance be seen in the table in Part a? In the graph? In the function rule(s) you selected in Part d? Payment #0 or (0, 580) y-intercept Start at value or y-int

Ellen: E = 480 – 20m Darryl: D = 480 – 40m Felicia: F = 360 – 20m 2. The diagram shows graphs of account balance functions for three Electric Avenue customers. D F Ellen: E = 480 – 20m Darryl: D = 480 – 40m Felicia: F = 360 – 20m a. Match each function rule with its graph. Explain how you could make the matches without calculations or graphing tool help (calculator). b. What do the numbers in the rules for Ellen’s and Felicia’s account balances tell you about the values of their purchases and their monthly payments? c. What do the numbers in the rules for Darryl’s and Felicia’s Slope and y-intercept differences. Different start amount, same spending rate. Different start amount, different spending rate.

Homework Check: CW1: Buying on Credit CW2: Buying / Selling on Credit WS HW: Hooke’s Law