The price elasticity of demand of Good X is half the price elasticity of demand of Good Y. A 25% rise in price of good Y reduces its demand from 400 to 300 units. Calculate percentage change in demand of Good X when its price falls from Rs 10 to Rs 8 per unit

e_p1= 1/2 e_p2............1

% change in price = 25 %

% change in demand = del dd/ dd * 100

  = 100/400 * 100

 = 25%

e_p2 = % change in price / % change in demand

  = 25 / 25

  = 1

from 1 = e_p1 = 1/2

% change in price = del p/p * 100

 = 2/10 * 100

  = 20 %

e_p1 = % change in price / % change in demand 

 1/2 = 20 / % change in demand

therefore % change in demand = 40%

hope this is helpful!!!!