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A cash register contains only dimes and quarters. There are $65$ coins equaling $\$12.80$ in the register. How many dimes and how many quarters are in the register?

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    Please use more descriptive titles. General subjects like "algebra" are covered by the tags; the title should be more specific to the question where possible.2011-09-22
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    Let the number of dimes be $x$ and the number of quarters $y$. There are two constraints: the total number of coins, and the total value. Write these down, and solve the system. If you get stuck, ask for another pointer2011-09-22
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    Say the number of dimes is $d$ and the number of quarters is $q$. (1) What does the fact there are 65 coins total tell you about $d$ and $q$ together? (2) If each dime contributes 0.10 to the total, and each quarter contributes 0.25 to the total, how can we represent the total value in terms of the number of dimes and quarters? (3) When we set this total value equal to 12.80, what equations are we left with and how should we solve them?2011-09-22
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    is there a way to do it with only 1 variable? we haven't learned to use 2 yet.2011-09-22
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    Ok, if you insist on using just 1 variable, here's a way. Suppose the number of dimes is $d$. Then what is the number of quarters in terms of $d$? Now, as @anon says, each dime contributes $0.10$ to the total amount, and each dollar contributes $0.25$. Can you represent the total amount in terms of the number of dimes and quarters? But you are given that the amount is $12.80$. So, ...2011-09-22
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    could I use d +.15 to represent quarters? i'm sorry i really have no clue what i'm doing...2011-09-22

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