Question 260793
Since the demand (d) relies on the price (p), the price (p) is the independent variable and the demand (d) is the dependent variable. You might have learned earlier that of the ordered pair (x,y), 'x' is the independent variable and 'y' is the dependent variable. 



From the slope formula {{{m=(y[2]-y[1])/(x[2]-x[1])}}}, we see that the y variables are placed in the numerator. This means that the dependent variables are in the numerator.


So this means that you should have the slope of {{{m=(30-50)/(300-200)=-20/100=-1/5=-0.20}}} (since the dependent variable 'd' should be in the numerator). Let me know if this helps.