Determine the Giffen goods - law of demand

An exception to this law is the distinctive case of Giffen goods named after Sir Robert Giffen (1837-1910). 'Giffen goods' doesn't represent any particular commodity. It could be any low-grade commodity that is cheap as compared to its superior alternatives, consumed usually by the lower income group families as a significant consumer good. If price of such goods rises (price of its alternative remaining stable), its demand heightensin place of falling.

For instance the minimum consumption of food grains by alower income group family per month is 30 kgs comprising 20 kgs of bajra (a low-grade good) at the rate of 10$ per kg and 10 kgs of wheat (a high quality good) at 20$ per kg. They have a fixed expenditure of 400$ on these items. Though if the price of bajra rises to 12$ per kg the family would be compelled to decrease the consumption of wheat by 5 kgs and add to that of bajra by same quantity so as to meet its minimum consumption requisite within 400$ per month. Undoubtedly, the family's demand for bajra rises from 20 to 25 kgs when its price rises.