Suppose that the demand equation for a certain item is $$p+2Q^{2}-150 = 0.$$

$p$ represents the price of an item and $Q$ represents the number of items sold at that price.

Evaluate the demand elasticity $E$ at $p=70$:

$E(70)$ =

Here, "demand elasticity" is the absolute value of $\displaystyle \frac{\text{percent change in quantity}}{\text{percent change in price}}$ for an infinitesimal change in price, so $$E = \left| \lim_{\Delta p \to 0} \frac{ \Delta Q / Q}{\Delta p / p} \right| \ .$$