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sally has 20 coins in her piggy bank,all dimes and quarters. The total amount of money is $3.05. How many of each coin does she have?
Sally has 20 coins in her piggy bank, so d + q = 20
The total amount of money is $3.05. Use the value of each coin multiplied by its number to get total value .10d + .25q = 3.05 multiply everything by 100 to clear the decimal places 10d + 25q = 305 and d + q = 20
solve the second equation above in terms of either d or q - lets do d d = 20 - q sub that into the first equation 10d + 25q = 305 10(20 - q) + 25q = 305 200 - 10q + 25q = 305 15q = 105 q = 105/15 = 7 and from above d = 20 - q = 20 - 7 = 13
so, there are 13 dimes and 7 quarters verify with orig problem 13 + 7 = 20, OK, and $1.30 + $1.75 = $3.05
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