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I REALLY NEED HELP ON THESE QUESTIONS!!!! IM SOOO STUCK!!!!

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 $15. The second mixture has 4 ounces of Sumatra and 12 ounces of Celebes Kalossi, and costs $21. How much does one ounce of Sumatra and one ounce of Celebes Kalossi cost?

Respuesta :

x = price Sumatra, y = price Celebes

12*x + 4*y=15

4*x + 12*y = 21

Now, solve it. For instance (there are many ways):

Multiply the second equation by (-3):

12*x + 4*y=15

-12*x  -36*y = -63

Sum them up (x cancel out. That's why we multiply by -3)

-32y=-48,  y = 48/32=6/4=3/2

y = 3/2 and x = go to any equation. Say the second again:

4*x + 12*y = 21

4x + 12*3/2 =21 ----> 4x + 18=21, 4x = 3, x = 3/4.

So cost of Sumatra $ 3/2  per oz, or $ 1.50

Cost of Celebes Kalossi (what a name!) $ 3/4 per oz = $ 0.75 per oz

Let's check it with the first equation:

12*0.75+4*1.5 = 15!

Clear?



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