(a) Related goods are of two types, Substitute goods and Complementary goods.
(i) In case of substitute goods: When price of one commodity falls, demand for other commodity declines, e.g., decrease in the price of coffee will decrease the demand for tea.
(ii) In case of complementary goods: When price of one commodity falls, demand for other commodity rises, e.g., decrease in the price of petrol will increase the demand for car.
(b) Change in the income of buyers also influences his demand for different goods. The demand for normal goods like full cream milk tends to increase with increase in income and vice-versa. On the other hand, the demand for inferior goods like coarse grain tends to decrease with increase in income and vice- versa.
