Question :

One Grand Father, One Father and One Grand Son.
Sum of their age is 140 Years.
Grand Son’s age in month is equal to Grand Father’s age in years.
Grand Son’s age in days is equal to Father’s age in weeks.
What is the Age of all three?

Answer :

Son’s age: 7 Years, Father Age: 49 Years and Grand Father’s Age: 84 Years.

Lets assume the age(in years) of Grand Father, Father and Son as GF, F and S respectively.
Sum of their age is 140 Years
=> Equation 1 => GF + F + S = 140
Grand Son’s age in month = Grand Father’s age in years
S12 = GF => Equation 2=> GF = 12S
Grand Son’s age in days = Father’s age in weeks
S365 = F*(365/7)
S = F/7 => Equation 3 => F = 7S

Now we have three variables and three equations, we can easily solve it
12S + 7S + S = 140
20s= 140 => S = 7
F = 7S = 49
GF = 12S = 84.