SOLUTION: If Rio coffee costs $5 a pound and Java cost $7.50 a pound, how many pounds of each must be bought to fill a 120-pound canister with a blend worth $7 a pound?

Question 1113692: If Rio coffee costs $5 a pound and Java cost $7.50 a pound, how many pounds of each must be bought to fill a 120-pound canister with a blend worth $7 a pound?
Answer by ikleyn(52781) (Show Source): You can put this solution on YOUR website!
.

 R +     J = 120        (1)    (R pounds of Rio and J pounds of Java)
5R + 7.50J = 7*120      (2)    ("money" equation)


Multiply eq(1) by 5 (both sides). Keep eq(2) as is:

5R +    5J = 5*120      (1')
5R + 7.50J = 7*120      (2')


Subtract eq(1') from eq(2'). In this way, you eliminate R and get a single equation for the unknown J:

7.50J - 5J = 7*120 - 5*120

2.5J = 240  ====>  J =  = 96.


Answer.  96 pounds of Java coffee and the rest  120-96 = 24 pounds of Rio coffee.

Solved.

On the way, you learned how the Elimination method works.

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