Question 1011837
Marina has a total of 21 coins in dimes and quarters. She has two times as many dimes as quarters 
a) define the variables
d = # of dimes ; q = # of quarters
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b) state the system of equations that model this situation
Quantity Eq:: d + q = 21
Quantity Eq:: d = 2q
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c) determine how many dime and quarters marina has
Substitute for "d" and solve for "q"::
2q + q = 21
3q = 21
q = 7 (# of quarters)
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Solve for "d"::
d = 21-q = 21-7 = 14 (# of dimes)
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d) how much money does marina have 
Ans: 7*25 + 14*10 = 175 + 140 = $3.15
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Cheers,
Stan H.
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