Can the demand curve be a rectangular hyperbola, but $E_D \neq 1$? So, I am given the next table:


I am asked to find $Q_D$.
So the prerequisites to find $Q_D$ is that the price must change, and all other factors of demand must be steady. So, I can find the $Q_D$ between A and C. Our professor stated that, as $P_A Q_A= P_C Q_C =20000$ , the demand curve is a rectangular hyperbola and $Q_D = \frac{20.000}{P}$. However, in the rectangular hyperbola, $E_D=-1$ in every point of the demand curve, but here we have that $E_{D}=-0,8$. Is there something I am missing? Does $E_D=-0.8  \neq -1$ imply that the curve is a line or not? Thanks!
Let's try a linear demand function, so $Q=a-bP$. Then $\epsilon_A=\frac{\partial Q}{\partial P}\frac{P_A}{Q_A}=-b\frac{P_A}{Q_A}$, so $b=-\epsilon_A\frac{Q_A}{P_A}=0.8\frac{500}{40}=10$. Then $a=Q_A+bP_A=500+10\cdot 40=900$. Thus, your table is compatible with the demand function $Q_D=900-10P$.