Question 1016199
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cindy has 17 bills in her wallet. some are $10 bills and some are $20 bills. the total value of the bills are $230. 
how many $10 bills and how many $20 bills does she have?
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Let x = # of $10 bills, and y = # of $20 bills.
Then you have the system of two equations in two unknowns

  x +   y =  17,   (1)
10x + 20y = 230.   (2)

Express x via y from equation (1): x = 17 - y, and substitute it into equation (2). You will get a single equation for y

10*(17-y) + 20y = 230.

Now simplify and solve:

170 - 10y + 20y = 230,

10y = 230 - 170 = 60.

y = {{{60/10}}} = 6.

Then x = 17 - y = 17 - 6 = 11.

<U>Answer</U>. 11 $10 bills and 6 $20 bills.
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