How would you calculate the Price Elasticity of Demand if the Prices are constant, given that there is change in quantity demanded? I have data that I have collected suggests that the prices are more or less constant throughout the month whereas the quantity demanded changes on a day to day basis. Recalling the formula for PED, we can write:

$$PED= {P*\Delta Q \over Q*\Delta P}$$ we can observe that $\Delta P=0$ as I mentioned earlier, giving us $PED=infinity$. However in reality the demand is inelastic. Is there a way to handle this error?

Assumption while measuring the prices: The supply was constant. 

These are tuples of the form (Price and Demand)

(275,30)

(275,80)

(275,20)

(275,70)

(282,0)

(282,50)

(282,100)

(282,80)
it does not make sense to use the formula for the elasticity like this.The PED is used for theoretical purposes in static equilibrium analisys. If you want to measure the elasticity empirically, then you must use the correct econometric technique, given your dataset.

One simple way is to run a linear regression (OLS) after a log-transform in your data. The parameter estimated captures de per cent sensibility of you endougeneos variable (demand) to your explicative varible (price). 

Don´t forget to check if the parameter statistical significance, you may need more data.