Answer: The average price is $72.166.
Step-by-step explanation:
Since we have given that
[tex]S(t) = t(25-5t)+18[/tex]
We need to find the average price of the stock over the first five years.
So, Average price would be
[tex]\dfrac{1}{b-a}\int\limits^a_b {t(25-5t)+18} \, dt\\\\ =\dfrac{1}{5}\int\limits^5_0 {25t-5t^2+18} \, dt\\\\ =\dfrac{1}{5}{\dfrac{25t^2}{2}-\dfrac{5t^3}{3}+18t|^5_0 \\\\=\dfrac{1}{5}[\dfrac{25\times 25}{2}-\dfrac{125}{3}+18\times 5]\\\\=\dfrac{1}{5}[312.5-41.67+90]\\\\=72.166[/tex]
Hence, the average price is $72.166.