Question 190900
Brianne received 9 bills, some twenties,some tens, and some fives, in exchange for a $100 bill. There was twice as many fives as there were tens. How many of each kind of bill did she receive? 
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Let x = number of tens
then
2x = number of fives
9-(x+2x) = number of twenties
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Since the total is $100:
10x + 5(2x) + 20(9-(x+2x)) = 100
10x + 5(2x) + 20(9-x-2x) = 100
10x + 5(2x) + 20(9-3x) = 100
10x + 10x + 180 - 60x = 100
180 - 40x = 100
-40x = -80
x = 2 (number of tens)
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number of fives:
2x = 2(2) = 4 
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number of twenties:
9-(x+2x) = 9-3x = 9-3(2) = 9-6 = 3 
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Answer:
2 tens, 4 fives, and 3 twenties