Which type of product is wheat for people from group A and people from group B?
Figure 1(wheat is a giffen good for group A)
Above figure shows that as the price for wheat increases demand for wheat decreases and whenever the price for wheat decreases, its demand decreases also because it is human mentality that higher cost products are better. Decrease in price will definitely decrease the demand for wheat. Demand decreases, price decreases, quantity decreases.
Above diagram shows downward sloping demand curve due to the presence of substitutes of wheat. Hence, when price for wheat decreases its demand increases and vice versa.
What will be the income effect for people from group A?