How does the budget line change, if the consumer's income increases to Rs. 40 but the prices remain unchanged ?
If the consumer's income increases to Rs. 40, then she can buy more of both the goods (combination of goods). It will shift the budget line upward, to the right from AB to A1,B1 but the new budget line will be parallel to the old budget line as there is no change in the slope of the budget line.