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Example

Interpreting the Slope and CC-Intercept of C=4p+25C = 4p + 25

Stella runs a home business selling gourmet pizzas. Her weekly cost is modeled by the linear equation C=4p+25C = 4p + 25, where CC is the weekly cost in dollars and pp is the number of pizzas sold. Although the equation uses CC and pp instead of yy and xx, it is still in slope-intercept form.

ⓐ Find CC when p=0p = 0:

C=4(0)+25=0+25=25C = 4(0) + 25 = 0 + 25 = 25

Stella's fixed cost is $25 per week when she sells no pizzas.

ⓑ Find CC when p=15p = 15:

C=4(15)+25=60+25=85C = 4(15) + 25 = 60 + 25 = 85

Stella's cost is $85 when she sells 15 pizzas.

ⓒ Interpret the slope and CC-intercept:

  • The slope is 44, which means the cost increases by $4 for each pizza Stella sells. This is the variable cost per pizza.
  • The CC-intercept is (0,25)(0, 25), which means that even when Stella sells no pizzas, her weekly costs are $25. This is the fixed cost.

ⓓ Graph the equation:

Because the CC-intercept is at 2525, a larger scale than the standard 10-10 to 1010 grid is needed. Start at the CC-intercept (0,25)(0, 25), then count out a rise of 44 and a run of 11 to locate a second point. Draw a straight line through the two points. The line passes through (0,25)(0, 25) and (15,85)(15, 85).

This example shows how the slope-intercept form applies to a business cost equation: the slope represents the per-unit variable cost, and the vertical-axis intercept represents the fixed cost.

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Updated 2026-05-03

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