Income(Rs.) 200. 240. 280. 320 Quantity. 50. 80. 100. 110 Calculate the income elasticity of demands..

Initial Income ($Y_1$) = Rs. 200
Final Income ($Y_2$) = Rs. 240
Initial Quantity ($Q_1$) = 50 units
Final Quantity ($Q_2$) = 80 units

The income elasticity of demand is $\boxed{3}$.

2. When income increases from Rs. 240 to Rs. 280:

Initial Income ($Y_1$) = Rs. 240
Final Income ($Y_2$) = Rs. 280
Initial Quantity ($Q_1$) = 80 units
Final Quantity ($Q_2$) = 100 units

The income elasticity of demand is $\boxed{1.5}$.

3. When income increases from Rs. 280 to Rs. 320:

Initial Income ($Y_1$) = Rs. 280
Final Income ($Y_2$) = Rs. 320
Initial Quantity ($Q_1$) = 100 units
Final Quantity ($Q_2$) = 110 units

The income elasticity of demand is $\boxed{0.7}$.