Question

The question says "The number of minutes included in different cell phone plans and the costs are shown in the table. What is the approximate rate of change in cost per minute?" Thanks for helping!

Answer 1

The expression for the rate of change is :

`\text{ Rate of Change = }(y_2-y_1)/(x_2-x_1)`

In the given question: x is the minutes and y is the cost

So consider any two consecutive set :

Let ( 38, 1000) & ( 50,1500)

`\begin{gathered} \text{Rate of Change=}\frac{Cost\text{ (2) -Cost(1)}}{Time(2)\text{ -Time(1)}} \\ \text{rate of Change=}(1500-1000)/(50-38) \\ \text{Rate of Change=}(500)/(12) \\ As\text{ the Highest common factor of 500 and 12 is 4 so :} \\ (500)/(12)=(125*4)/(3*4) \\ (500)/(12)=(125)/(3) \\ \text{Rate of Change=}(125)/(3) \end{gathered}`

Answer : 125/3