Linear Relationships, SM-Bank 028

A weekly gym membership can be purchased for different numbers of classes, as shown in the table below.

Number of classes	1	2	3	4
Cost in dollars	42	72	102	132

What is the rule connecting the number of classes purchased and the cost in dollars? (2 marks)

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$\text{Cost in dollars}=30\times \text{Number of classes}+12$

Show Worked Solution

$\text{Firstly, look at the increase in the cost with each additional class }$

$\longrightarrow\ 42 , 72 , 102 , 132\ \ \longrightarrow\text{The cost increases by }$30\text{ every class}$

$\text{Secondly, if we look at the difference between }42\ \text{and }30\ \text{in the first class}$

$\text{we get }12\text{ which needs to be added to each membership}$

$\therefore\ \text{Rule: Cost in dollars}=30\times \text{Number of classes}+12$