Question 1196797
This year, alex's grandfather's age is 6 times of Alex's age.
 After a few years, Alex's grandfather's age will be 5 times of Alex's age.
 After another few years, Alex's grandfather's age will be 4 times of Alex's age.
 What is Alex's grandfather's age this year?
:
let a = Alex's present age
Grandfather is 6 time Alex's, therefore:
let 6a = grandfathers present age
:
let y = "another few years"
let x = a few more years
:
"another few years" equation
6a + y = 5(a+y)
6a + y = 5a + 5y
6a - 5a = 5y - y
a = 4y
:
a "few more years" equation
6a + x = 4(a+x)
6a + x = 4a + 4x
6a - 4a = 4x - x
2a = 3x
a = 1.5x
:
a = a, therefore
4y = 1.5x
we want integers here, therefore
8y = 3x 
y = {{{3/8}}}x
y and x have to be single digit integers therefore
y = 3 yrs and x = 8 yrs
: 
find a
a = 4y
a = 4(3)
a = 12 yrs is Alex's age
then
6(12) = 72 yrs is grandfather's age

You can substitute in the 3 yr and 8 yr equations to confirm this