($$1999$$ Math League, Grade $$5$$, Question \#$$16$$)  The average of two odd numbers is always ． 
Overseas Competition->Knowledge Point->Number Theory Modules->Odd and Even Numbers->Odd and Even Applications
Avg of $$1$$ \& $$5$$ is $$3$$. Avg of $$1$$ and $$7$$ is $$4$$. Both are whole numbers. 