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AlgebraEasyEvaluating a linear model in context

Algebra practice question

A taxi company charges a fixed pick-up fee of $3 plus $2 for each mile travelled. The total cost of a trip, in dollars, is given by C(m) = 3 + 2m, where m is the number of miles travelled.

What is the total cost of a trip of 7 miles?

  1. A. $14
  2. B. $17Correct
  3. C. $21
  4. D. $35

Answer: B. $17

Substitute 7 for m: C(7) = 3 + 2(7) = 3 + 14 = 17 dollars. The $3 is paid once for the trip, and the $2 applies to each of the 7 miles.

Why the other answers are wrong

A. $14
$14 is 2(7), the mileage charge on its own. You left out the $3 pick-up fee, which is added to every trip.
C. $21
You used the $3 as the per-mile rate: 3(7) = 21. The $3 is charged once, and $2 is the amount charged per mile.
D. $35
You added the fee to the rate before multiplying: (3 + 2)(7) = 35. The pick-up fee is added once at the end, not to every mile.

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