SOLUTION: Mary emptied the change in the bottom of her purse. She found all quarters and dimes, worth a total of $10.25. The number of quarters was 7 less than twice the number of dimes. How

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Question 263592: Mary emptied the change in the bottom of her purse. She found all quarters and dimes, worth a total of $10.25. The number of quarters was 7 less than twice the number of dimes. How many of each type of coin did she have?
Answer by drk(1908) About Me  (Show Source):
You can put this solution on YOUR website!
This is a money equation. We need two equations.
(i) 10d+%2B+25q+=+1025
(ii) q+=+2d+-+7
step 1 - substitute (ii) into (i) to get
(iii) 10d+%2B+25%282d-7%29+=+1025
step 2 - distribute to get
(iv) 10d+%2B+50d+-+175+=+1025
step 3 - combine like terms to get
(v) 60d+-175+=+1025
add 175 to get
(vi) 60d+=+1200
d = 20
and from (ii)
q = 33