SOLUTION: 20. Suppose that income is a function of age. The following function represents the relation between average annual income l and age a. l(a)=-55a^2+5117a-54,421 (A) For wha

Algebra ->  Customizable Word Problem Solvers  -> Numbers -> SOLUTION: 20. Suppose that income is a function of age. The following function represents the relation between average annual income l and age a. l(a)=-55a^2+5117a-54,421 (A) For wha      Log On

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Question 1114738: 20.
Suppose that income is a function of age. The following function represents the relation between average annual income l and age a.
l(a)=-55a^2+5117a-54,421
(A) For what age does average income l equal $40,000?
(B) For what age does average income l equal $60,000?
(a) Average income l is equal $40,000 for the age of?
Answer by josgarithmetic(39625) About Me  (Show Source):
You can put this solution on YOUR website!
For part (A)
-55a%5E2%2B5117a-54421=40000
-55a%5E2%2B5117a-94421=0
General solution for quadratic equation:
a=%28-5117%2B-+sqrt%285117%5E2-4%2A%28-55%2A%28-94421%29%29%29%2F%28-2%2A55%29
a=%28-5117%2B-+sqrt%285117%5E2-4%2A55%2A94421%29%29%2F%28-2%2A55%29
a=%285117%2B-+sqrt%285117%5E2-4%2A55%2A94421%29%29%2F%282%2A55%29

a=%285117%2B-+sqrt%285411069%29%29%2F%282%2A55%29
Compute this and take the value which makes sense.