Question 694902
Given that a father's age is 1 less than twice that of his son,
 and that the digits AB making up the father's age are reversed in the son's age 
(i.e. BA).
How old are the father and son?
:
Let a = the 10's digit of father's age
Let b = the ones
then
(10a+b) = his age
and
(10b+a) = son's age (digits reversed
:
"Given that a father's age is 1 less than twice that of his son,"
10a + b = 2(10b+a) - 1
10a + b = 20b + 2a - 1
combine like terms
10a - 2a = 20b - b - 1
8a = 19b - 1
divide by 8
a = {{{19/8}}}b - {{{1/8}}}
Find a single digit value for b that will give an integer value for a
After a couple of attempts came up with: 
b = 3
a = {{{19/8}}}(3) - {{{1/8}}}
a = {{{57/8}}} - {{{1/8}}}
a = {{{56/8}}}
a = 7
then
Dad's age = 73
Son's age = 37
:
Check that: 2(37) - 1 = 73