Question

A store is selling two mixtures of coffee beans in one-pound bags. The first mixture has 12 ounces of Sumatra combined with 44 ounces of Celebes Kalossi, and costs $42. The second mixture has 44 ounces of Sumatra and 12ounces of Celebes Kalossi, and costs $30. How much does one ounce of Sumatra and one ounce of Celebes Kalossi cost?

Answer 1

Create 2 equations for the given problem

12s + 44c = 42
44s + 12c = 30

Take either equation and solve for either s or c.
12s + 44c = 42
12s = 42 - 44c
s = (42 - 44c) / 12
s = (21 - 22c) / 6

Substitute into 2nd equation

44s + 12c = 30
22((21 - 22c) / 3) + 12c = 30
22(21 - 22c) + 36c = 90
-448c +462  = 90
-448c = -372
c = -372/-448
c = 93/112
c = 0.83

Substitute into the 2nd equation

44s + 12c = 30
44s = 30 - 12c
s = (30 - 12 (93/112)) / 44
s = (30 - 279 / 28) / 44)
s = (30 - 9 27/28) / 44
s = 0.46

Prove
12s + 44c = 42
12(0.46) + 44(0.83) = 42
5.52 + 36.52 = 42
42.04 = 42

44s + 12c = 30
44(0.46) + 12(0.83) = 30
20.24 + 9.96 = 30.16

Assuming minor rounding issues this looks accurate.