Question

the phone company ringular has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone. if a customer uses 500 minutes, the monthly cost will be $220. if the customer uses 870 minutes, the monthly cost will be $368. a) find an equation in the form y = mx + b, where x is the number of monthly minutes used and y is the total monthly of the ringular plan. answer: y = do not use any commas in your answer. b) use your equation to find the total monthly cost if 798 minutes are used. answer: if 798 minutes are used, the total cost will be dollars. question help: video submit question

Explanation:

Step1: Find the slope $m$

The two - point formula for slope $m=\frac{y_2 - y_1}{x_2 - x_1}$. Let $(x_1,y_1)=(500,220)$ and $(x_2,y_2)=(870,368)$. Then $m=\frac{368 - 220}{870 - 500}=\frac{148}{370}=0.4$.

Step2: Find the y - intercept $b$

Substitute $m = 0.4$, $x = 500$ and $y = 220$ into $y=mx + b$. So $220=0.4\times500 + b$. Then $220 = 200 + b$, and $b=220 - 200=20$.

Step3: Write the equation

The equation is $y = 0.4x+20$.

Step4: Find the cost for 798 minutes

Substitute $x = 798$ into $y = 0.4x+20$. Then $y=0.4\times798+20=319.2 + 20=339.2$.

Answer:

A. $y = 0.4x+20$
B. 339.2