Question number

1.3 Linear Equations in Two Variables - Writing equations from data/points
0:00
Number of cars Maximum number of passengers and crew
3 174
5 284
10 559

The table shows the linear relationship between the number of cars, c , on a commuter train and the maximum number of passengers and crew, p , that the train can carry. Which equation represents the linear relationship between c and p ?

A.

55c-p=-9

B.

55c-p=9

C.

55p-c=-9

D.

55p-c=9

Number of cars Maximum number of passengers and crew 3 174 5 284 10 559 The

Hard-difficulty · SAT Math · Linear Equations in Two Variables — Writing equations from data/points. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice A is correct. It's given that there is a linear relationship between the number of cars, c , on a commuter train and the maximum number of passengers and crew, p , that the train can carry. It follows that this relationship can be represented by an equation of the form p=mc+b, where m is the rate of change of p in this relationship and b is a constant. The rate of change of p in this relationship can be calculated by dividing the difference in any two values of p by the difference in the corresponding values of c . Using two pairs of values given in the table, the rate of change of p in this relationship is 284-1745-3, or 55 . Substituting 55 for m in the equation p=mc+b yields p=55c+b. The value of b can be found by substituting any value of c and its corresponding value of p for c and p , respectively, in this equation. Substituting 10 for c and 559 for p yields 559=5510+b, or 559=550+b. Subtracting 550 from both sides of this equation yields 9=b. Substituting 9 for b in the equation p=55c+b yields p=55c+9. Subtracting 9 from both sides of this equation yields p-9=55c. Subtracting p from both sides of this equation yields -9=55c-p, or 55c-p=-9.

Choice B is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.