Question

This is from one of my Brain Teasers books:
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 ?

Answer 1

Since nobody will help me, I figured it out myself and I hope it's right!

Let m be the grandmother's age in years. If s is the son's age in years, then the son is 52s weeks old. If g is the grandson's age in years, then the grandson is 365g days old. Thus,
365g = 52s.
Since the grandson is 12g months old,
12g = m.
Since the grandson, the son and the grandmother together are 120 years,
g + s + m = 120.
The above system of 3 equations in 3 unknowns (g, s and m) can be solved as follows.
m / 12 + 365 m / (52 x 12) + m = 120 or
52 m + 365 m + 624 m = 624 x 120 or
m = 624 x 120 / 1041 = 72.
So, the grandmother is 72 years old.

Answer 2

@Kevin Solved another one by myself :(

Answer 3

XD