Rita was 25 when her first son was born. Today the sum of their ages is 105. How old is Rita and her son?
Let the son's age today be S
>>...Rita was 25 when her first son was born...<<
This tells us that Rita is 25 years older than her son,
therefore,
Rita's age today is (S+25)
>>...Today the sum of their ages is 105...<<
Rita's age today + Son's age today = 105
(S+25) + S = 105
Solve that and get S = 40.
So the son is 40 and Rita is 25 years older or 65.
Checking:
40 years ago the son was just born and Rita was 25.
Edwin