Joylin is writing an equation to model the proportional relationship between y, the total cost in dollars of downloading videos from a website, and x, the number of videos downloaded. She knows that the total cost to download 3 videos was $12. Her work to find the equation is shown below. Joylin’s Work Step 1 x=3/12=0.25 Step 2 y=0.25x Where did Joylin make her first error? Joylin divided 3 and 12 instead of multiplying the two numbers. Joylin computed the decimal equivalent of 3/12 incorrectly. Joylin used 0.25 as the coefficient of x instead of a product of x and y. Joylin switched the numerator and the denominator when she found k.

Solution:

Joylin switched the numerator and the denominator when she found k.

Joylin should divide 12/3 and not 3/12. As, y is total cost and x is number of videos.

For x=1, number of videos=1, y,or total cost=1*4=4,

For x=2,y=2*4=8

For x=3, y=3*4=12

So, the constant, k=4

So, Answer: Option (D)

Joylin switched the numerator and the denominator when she found k.

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