Question: An indifference curve plots the amounts x of product X and the amount y of product Y such that the value to a consumer of the total amount of products X and Y for any point along the curve is constant. It has the property that y decreases as x increases. For one consumer, good X is flour, good Y is sugar, x and y are in pounds, and 5 pounds of flour alone have the same value as 3 pounds of sugar alone. Which of the following could represent the indifference curve in the xy-plane for this consumer?
How do I know the value to a consumer of the total amounts of X and Y on a curve? How do I know it is constant when I look at a graph? How do the points (5,0) and (0,3) as shown in the answer explanation show that 5 pounds of flour alone and 3 pound of sugar alone have the same value?
The first graph you show, (A), includes the points (0,5) (0 lbs of sugar and 5 lbs of flour) and (3, 0) (3 lbs of sugar and 0 pounds of flour). You know that every point on that curve have the same value to a consumer because you are told this curve is an "indifference" plot- that this curve consists of (x, y) points such that x pounds of sugar and y pounds of four have the same value to the consumer.