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Question 1114741: 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?
(b) Average income l is equal $60,000 for the age of?
Answer by greenestamps(13203)   (Show Source):
You can put this solution on YOUR website!
The graph is a downward opening parabola, so it is likely that there will be two different ages for which the average income is $40,000 and two other different ages for which it is $60,000.
With "ugly" coefficients like in this problem, you don't want to be solving the problem with pencil and paper. Use a graphing calculator or some other mathematical tool to solve the problem.
I use a TI83 graphing calculator; I can graph the given equation and the two constant functions 40000 and 60000 and find where the graphs intersect.
Here is what the graph should look like....
Apparently the average income is $40,000 at about ages 24 and 68; it is $60,000 at about ages 36 and 54.
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