Alan is $5$ years old, his mother is $18$ years older than him, and his father is $2$ years older than his mother. How old is his father?~(adapted from $$2005$$ Math kangaroo Problems, Level $$1-2$$, Question \#$$7$$) 
Overseas Competition->Knowledge Point->Word Problem Modules->Age Problems->Basic Relationships in Age Problems->Difference of Ages
Alans\textquotesingle{} mother is $18$ years older than him, his mother is $23$ years old.  His father is two years older than his mother, so he is $25$ years old. 