At the price of ? 20, quantity demanded is 40 units. If price increases by ? 10, price
elasticity of demand is 0.4. Calculate the final quantity demanded.

Dear student,
elasticity of demanded =       Price      x    Change in quantity
                                             Quantity                              change in price

 0.4   =  20 / 40 x  change in quantity / 10

0.4  = 0.5 x  change in quantity /10
0.4 x 10 =  0.5 x change in quantity
4 = 0.5 x change in quantity
4/0.5 = change in quantity
8 = change in quantity

So, final quantity = 8

Regards