Linear Relationships, SM-Bank 027

A surfboard can be hired for different numbers of hours, as shown in the table below.

Number of hours	1	2	3	4
Cost in dollars	35	50	65	80

What is the rule connecting the number of hours of surfboard hire and the cost in dollars? (2 marks)

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$ Cost in dollars}=15\times \text{Number of hours}+20$

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$\text{Firstly, look at the increase in the cost with each hour of hire }$

$\longrightarrow\ 35 , 50 , 65 , 80\ \ \longrightarrow\text{The price increases by }$15\text{ every hour}$

$\text{Secondly, if we look at the difference between }35\ \text{and }15\ \text{in the first hour}$

$\text{we get }20\text{ which needs to be added to each hiring fee}$

$\therefore\ \text{Rule: Cost in dollars}=15\times \text{Number of hours}+20$