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My grandson is about as many days as my son in weeks, and my grandson is as many months as I am in years. My grandson, my son and I together are 120 years. Can you tell me my age in years ?

It's really simple : The above system of 3 equations in 3 unknowns can be solved as follows.

I know the solution should i write it ?

Manal
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    if you know the answer why post this question? this isn't very interesting either. then why? – Guy Mar 12 '14 at 21:29
  • I thought i have the right to post a question that i already know the answer of it – Manal Mar 12 '14 at 21:30
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    I guess you do, but the convention is that you only post a question when you need help, or when you think that posting this question will help someone else, i.e, add value to the community. this is neither. – Guy Mar 12 '14 at 21:32

2 Answers2

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Assuming $x, y,\text{ and } z$ are the ages of your grandson, your son, and you respectively, expressed in years, then your system is:

$$365x = 52y$$ $$12x=z$$ $$x+y+z=120$$

Therefore $x=6$, $y=42$ and $z=72$

dakisbac
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Your son is $7$ times as old as your grandson. You are $12$ times as old as your grandson. Therefore if you let $x$ denote the age of your grandson, you have $$x + 7x + 12x =20x = 120$$ It follows that your grandson is $6$ years old, your son is $42$ years old and you are $72$ years old.

EuYu
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