Given.
Percentage fall in demand = 20
Initial Price= Rs.10
New Price =Rs.12
% Increase in Price=2/10x100=20%
We know,
Ed=% Change in Denrand / % Change in Price
=-20/20=-1
Now, if price rises from 10 to 13
% Change in Price =3/10x100=30%
So,
% Change in Demand = % Change in Price x Ed = 30 x-1 =- 30
So, we can say that if the price rises from Rs.10 to Rs.13, i.e.by 30%, then the demand will fall by 30%. This is because the goods follows unitary elasticity,.