SOLUTION: Owyn just bought some $.39, $.24, and $.13 stamps at the post office. The 100 stamps cost $33.40, and there were twice as many $.24 stamps in the sale as there were $.13 stamps. Ho

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Question 1109457: Owyn just bought some $.39, $.24, and $.13 stamps at the post office. The 100 stamps cost $33.40, and there were twice as many $.24 stamps in the sale as there were $.13 stamps. How many stamps of each denomination did Owyn buy?
Answer by ikleyn(52921)   (Show Source): You can put this solution on YOUR website!
.
Let x be the number of the 13-cent stamps.


Then the number of the 24-cent stamps is 2x,  and

     the number of the 39-cent stamps is (100-2x-x) = (100-3x).


The "money equation" is

    13x + 24*(2x) + 39*(100-3x) = 3340    cents.


13x + 48x + 3900 - 117x = 3340,

-56x = 3340 - 3900 = -560   ====>  x =  = 10.


Answer.  10  13-cent stamps;  20  24-cent stamps  and  100-10-20 = 70 39-cent stamps.


Check.    10*13 + 20*24 + 70*39 = 3340  cents.   ! Correct !


The lesson to learn from this solution. 
    This problem is reduced to a single equation in one unknown.

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To see other similar solved problem by the same method,  look into the lesson
    - More solved word problems on a single linear equation
in this site.


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