My grandson is about as many days as my son is weeks, and my grandson is as many months as I am in years. My grandson, my son and I together are 140 years. Can you tell me my age in years?

The first equation (365g = 52s) can be approximated by
7g = s.

As before, the other two equations are
12g = m
g + s + m = 140.

The above system of 3 equations in 3 unknowns (g, s and m) can be simply solved as follows.
g + 7g + 12g = 140 or 20g = 140.
m = 12g = 12 × 140 / 20 = 84.

So, Grandpa is 84 years old.

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