Question 950415
Mary is 12 years and her father is 42 years old 
how old was her father when he was 4 times as old as mary?
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Equations:
f = m + 30
42+x = 4(12+x)
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42+x = 48+4x
3x = -6
x = -2
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When father was 40, mary was 10.
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Cheers,
Stan H.
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