Question

The sale price of apples at a local grocery store is $1.35 for the first pound and $1.10 for each additional pound. Which function rule shows how the cost of apples, y, depends on the number of pounds, x?

1.)y = 1.10(x – 1) + 1.35
2.)y = 1.10x + 1.35
3.) y = 1.35x + 1.10
4.)y = (1.10 + 1.35)x

Answer 1

1.) y = 1.10(x – 1) + 1.35

Explanation:

When x pounds of apples are purchased, the number of "additional" pounds is (x-1). The cost of those additional pounds is then added to the cost of the first pound to get ...

y = 1.10(x -1) +1.35

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Comment on the function rule

Personally, I think it is easier to write the rule as y = 1.10x +0.25, considering the first pound to have a $0.25 premium added to its otherwise $1.10 cost. This saves an operation when evaluating the formula for some value of x.