Question 302928
A collection of dimes and quarters is worth $25. There are 40 more dimes than quarters. How many of each are there? 
Let d=dimes
q=quarters 
I came up with these two equations put they didn't work out: 
10d + 25q = 25 
40 + q = d
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One slip:
10d + 25q = 2500
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Smack yourself in the forehead, then you can finish it.