Question 133181
1. If John is x years old and Julia is 4 years younger, what age does Alfred have in each case? 
John is x
Julia is x-4
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a) Alfred is 1 year older than the average age of John and Julia.
Alfred = [(x + x-4)/2] + 1  = [(2x-4)/2] + 1  = x-2 + 1 = x-1 
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b) Alfred is 2 years younger than 5 times the difference of John's and Julias ages.
EQUATION:
x-1 =5(x-(x-4)) -2 = 20-2 = 18
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This math text is in Spanish so I translated the problems into English. 
2. A father is 3 times as old as his son. In 12 years he will be double the age of his son. What are the father and son's ages now?
Let son's age be "x"; Father's age is "3x".
In 12 yrs, son will ber x+12; father will be "3x+12"
EQUATION:
3x+12 = 2(x+12)
x = 12 (son's age)
3x= 36 (father's age)
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Cheers,
Stan H.