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What is the answer to this Quadratic functions question? ?

The average annual income I, in dollars, of a lawyer with an age of x years is modeled with the following function: 

I = - 425 x ^2 + 45,500 x - 650,000

According to this model, at what average age do lawyers earn their maximum average annual income. 

Round to the nearest year.

I understand this concept but I think Im missing an important step.

I really appreciate the help.

1 Answer

Relevance
  • 6 months ago

    Differentiate and equate to zero 

    I =  - 425 x ^2 + 45,500 x - 650,000

    dI/dx = 2(-425)x + 45500 = 0 

    850x = 45500

    x = 45500 / 850 

    x = 4550 / 85 

    x = 910/17

    x = 53.929 years. 

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