Question

A store is selling two mixtures of coffee beans in one-pound bags. The first mixture has 12 ounces of Sumatra combined with 4 ounces of Celebes Kalossi, and costs $32. The second mixture has 4 ounces of Sumatra and 12 ounces of Celebes Kalossi, and costs $40. How much does one ounce of Sumatra and one ounce of Celebes Kalossi cost?

Answer 1

We let x as the cost of one ounce of Sumatra and y as the cost of one ounce of Celebes Kalossi. For mixture 1, we have 12x + 4y = 32 and for mixture b, we have 4x + 12y = 40

First, Multiply eq. 1 by 4
4(12x + 4y = 32)4        ⇒    36x + 12y = 96

We now have 
(36x + 12y = 96) – (4x + 12y = 40)
X = 1.75     ⇒ cost of one ounce of Sumatra 

Substitute x to either equation to get the value of y
12(1.75) + 4y = 324
y = 32-21
4y = 11
Y = 2.75     ⇒ cost of one ounce of Celebes Kalossi