Question 1167121
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Mary bought 10 gift cards in The denominations of $20, $50,$100. She spent $370. 
She has twice as many $20 gift cards as $50 gift cards. How many of each denomination of gift card did she buy? 
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<pre>
Let x be the number of $50 cards.


Then the number of the $20 cards is 2x, and the number of the $100 cards is  (10-x-2x) = (10-3x).


Now you can write the money equation


    50x + 20*(2x) + 100*(10-3x) = 370  dollars.


Simplify and solve


    50x + 40x + 1000 - 300x = 370

    1000 - 370 = 300x - 50x - 40x

     630       = 210x

       x       = 630/210 = 3.


<U>ANSWER</U>.  3  $50-cards;  3*2 = 6  $20-cards  and  the rest  10- 3 - 6 = 1  $100-card. 
</pre>

Solved  &nbsp;&nbsp;&nbsp;&nbsp;// &nbsp;&nbsp;using only one equation in one unknown.