If you spent your entire income, you could afford either 3 units of x and 9 units of y or 9 units of x and 3 units of y.If you spent your entire income on x, how many units of x could you buy?
A)21
B)16
C)12
D)There is not enough information to determine the number of x.
E)None of the above.

Question

Quizplus · Accepted Answer

Let's assume that the income is $1. 
If you spend it on 3 units of x and 9 units of y, the cost of unit x would be 1/3 and the cost of unit y would be 1/9. 
Similarly, if you spend it on 9 units of x and 3 units of y, the cost of unit x would be 1/9 and the cost of unit y would be 1/3. 
Now, if you spend the entire income on x only, the cost of unit x would be the same as the cost of the x unit in the scenario where you spent the entire income on 9 units of x and 3 units of y. So, the cost of one unit of x would be 1/9. 
Therefore, you could buy 9 units of x if you spend your entire income on x.

If You Spent Your Entire Income, You Could Afford Either