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$$y=19.99+1.50 x$$The equation above models the total cost $y$, in dollars, that a company charges a customer to rent a truck for one day and drive the truck $x$ miles. The total cost consists of a flat fee plus a charge per mile driven. When the equation is graphed in the $x y$-plane, what does the $y$-intercept of the graph represent in terms of the model?

SAT · Math · previous-year question

  1. A.A flat fee of $\$ 19.99$correct
  2. B.A charge per mile of $\$ 1.50$
  3. C.A charge per mile of $\$ 19.99$
  4. D.Total daily charges of $\$ 21.49$

Answer

A. A flat fee of $\$ 19.99$

Explanation

Choice A is correct. The $y$-intercept of the graph of $y=19.99+1.50 x$ in the $x y$-plane is the point on the graph with an $x$-coordinate equal to 0 . In the model represented by the equation, the $x$-coordinate represents the number of miles a rental truck is driven during a one-day rental, and so the $y$-intercept represents the charge, in dollars, for the rental when the truck is driven 0 miles; that is, the $y$-intercept represents the cost, in dollars, of the flat fee. Since the $y$-intercept of the graph of $y=19.99+1.50 x$ is $(0,19.99)$, the $y$-intercept represents a flat fee of $\$

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