1p^2 \), we have already calculated the derivative to be \( f'(p) = -4 - 0.2p \).
Now, substitute \( p = 65 \) into the derivative:
\[ f'(65) = -4 - 0.2(65) = -4 - 13 = -17 \]
Now, calculate the elasticity of demand using the formula \( E = \frac{p}{f'(p)} \):
\[ E
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