Question
Let $$W$$ denote the words in the English dictionary. Define the relation $$R$$ by $$R = \left\{ {\left( {x,y} \right)} \right. \in W \times W$$ the words $$x$$ and $$y$$ have at least one letter in common.} Then $$R$$ is
A.
not reflexive, symmetric and transitive
B.
reflexive, symmetric and not transitive
C.
reflexive, symmetric and transitive
D.
reflexive, not symmetric and transitive
Answer :
reflexive, symmetric and not transitive
Solution :
Clearly $$(x, x)$$ $$ \in R\,\forall x \in W.$$ So $$R$$ is relexive.
Let $$(x, y)$$ $$ \in R,$$ then $$(y, x)$$ $$ \in R$$ as $$x$$ and $$y$$ have at least one letter in common. So, $$R$$ is symmetric.
But $$R$$ is not transitive for example
Let $$x$$ = INDIA, $$y$$ = BOMBAY and $$z$$ = JOKER
then $$(x, y)$$ $$ \in R$$ ($$A$$ is common) and $$(y, z)$$ $$ \in R$$ ($$O$$ is common) but $$(x, z)$$ $$ \notin R.$$ (as no letter is common)