Lila wrote an equation of the cost for printing brochures, where x represents the number of brochures and y represents the total cost. The total cost for 35 brochures is $41.45. The total cost for 65 brochures is $55.55.

Question

Step 1: Write the ordered pairs (35, 41.45) and (65, 55.55).

Step 2: Find the slope. m = StartFraction 55.55 minus 41.45 Over 65 minus 35 EndFraction = 0.47

Step 3: Find the y-intercept to write the equation in slope intercept form. y minus 55.55 = 0.47 (x minus 35). Y minus 55.55 = 0.47 x minus 16.45. y = 0.47 x + 39.1.

Which explains the error that Lila made?
Lila made in error in Step 1 by reversing the ordered pairs.
Lila made an error in Step 2 by not using the slope formula.
Lila made an error in Step 3 when she did not use the x- and y-coordinates from the same ordered pair.
Lila made an error in Step 3 when she did not use the distributive property correctly when multiplying.

Answer 1

Lila made an error in Step 3 when she did not use the x- and y-coordinates from the same ordered pair.

In her calculation for finding the y-intercept, she used the point (35, 41.45) and (65, 55.55) correctly to find the slope, but when determining the equation of the line, she should have substituted one of the ordered pairs into the point-slope formula using the correct y-coordinate corresponding to the x-coordinate she chose. She incorrectly substituted values when calculating the y-intercept, leading to the wrong slope-intercept equation.

Thus, the correct answer is: Lila made an error in Step 3 when she did not use the x- and y-coordinates from the same ordered pair.