Question 364533
Audrey has 32 dimes and quarters in her piggy bank with a total value of 6.50. How many of the coins are dimes and how many are quarters? 
I need to write 2 equations and solve by addition method
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Let x = number of dimes
and y = number of quarters
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From: "Audrey has 32 dimes and quarters in her piggy bank"
x + y = 32 (equation 1)
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From: "total value of 6.50"
.10x + .25y = 6.50 (equation 2)
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Using the "addition method", to eliminate x, we multiply both sides of equation 1 by -.10 and "add" the two equations together:
-.10x - .10y = -3.2
.10x + .25y = 6.50
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      .15y = 3.3
y = 22 (number of quarters)
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Substitute the above value of y back into equation 1 to find x:
x + y = 32
x + 22 = 32
x = 32-22
x = 10 (number of dimes)