You can put this solution on YOUR website! Same problem, different numbers:
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Carmen is 12 years old ??? than David. Five years ago the sum of their ages was 28. How old are they now?
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Carmen is 12 years older than David. Five years ago the sum of their ages was 28. How old are they now?
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The sum of their ages now is 38.
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C + A = 38
C - A = 12
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