Question 700682
The Lee's have three children. The oldest is twice as old as the youngest. The middle child is five years older than the youngest. If the sum of the age is 57, how old is each child?
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Let oldest be "a"
middle be "b"
youngest be "c"
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Equations: 
a = 2c
b = c+5
a + b + c = 57
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Substitute for "a" and "b":
2c + c+5 + c = 57
4c = 52
c = 13 years (youngest)
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a = 2c = 26 years (oldest)
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b = c+5 = 18 years (middle)
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Cheers,
Stan H.