Question 1114741
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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.<br>
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.<br>
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.<br>
Here is what the graph should look like....<br>
{{{graph(400,400,0,80,-20000,100000,-55x^2+5117x-54421,40000,60000)}}}<br>
Apparently the average income is $40,000 at about ages 24 and 68; it is $60,000 at about ages 36 and 54.