Question 1115647
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                Again, typical problem to solve using  SINGLE  unknown.



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Let x = amount of hazelnut (in pounds).

Then the amount of mocha coffee is the same x pounds.

Then the amount of vanilla-flavored coffee is (10-2x) pounds.


The money equation is

12*(10-2x) + 13.50x + 15x = 138,   or


120 - 24x + 28.5x = 138,

4.5x = 138 - 120 = 18  ====>  x = {{{18/4.5}}} = 4 pounds.


<U>Answer</U>.  4 pounds of hazelnut;  4 pounds of mocha coffee;  and  2 pounds of vanilla-flavored coffee.
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Solved.