Question 1198772
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Let x be the Freddy grandson's age.


Then Freddy's age is (6x+3) years.


The problem says that

    x + (6x+3) > 67.


It implies

    7x > 67 - 3

    7x >   64

     x >   64/7 = 9{{{1/7}}}.


Since the age is an integer number of years, from the last inequality we can conclude that x >= 10.


In other words, Freddy's grandson is at lest 10 years old.


10 years is the youngest age of the Freddy's grandson.
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Solved.