Question 150714
3m + 4c + 7d = 5.45
4m + 2c + 8d = 5.30
2m + 5c + 6d = 5.15 
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subtract 3rd equation from 1st to get:
 m -  c +  d = 0.30
4m + 2c + 8d = 5.30
2m + 5c + 6d = 5.15 
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subtract 4 times 1st from 2nd; 
subtract 2 times 1st from 3rd:
 m -  c +  d = 0.30
 0 + 6c + 4d = 4.10
 0 + 7c + 4d = 4.55
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interchange 2nd and 3rd to get:
m -  c +  d = 0.30
0 + 7c + 4d = 4.55
0 + 6c + 4d = 4.10
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subtract 3rd from 2nd to get:
m -  c +  d = 0.30
0 +  c +  0 = 0.45
0 + 6c + 4d = 4.10
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At this point you can see that c = 0.45
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Subtitute that into the 3rd equation to solve for "d":
6(0.45) + 4d = 4.10
2.7 + 4d = 4.10
4d = 1.40 
d = 0.35
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Substitute the values of c and d into the 1st equation to solve for "m":
m - 0.45 + 0.35 = 0.30
m - 0.10 = 0.30
m = 0.40
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one mild costs 40 cents
one coffee costs 45 cents
one doughnut costs 35 cents
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Cheers,
Stan H.