Question 511964
f = number of frogs
4f = number of frogs' legs
d = number of ducks
2d = number of ducks' legs
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f = d+6
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4f + 2d = 54
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substitute f=d+6
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4(d+6) +2d =54
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4d +24 +2d = 54
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6d = 30
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d = 5
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f = d+6 = 5+6 = 11
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Check to see how many legs you have:
4(11) = 44
2(5) = 10
44+10 = 54
OK.
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Answer:  There are 5 ducks and 11 frogs.
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Done.