Can anybody give me a description about this?

Question

If $x \in A$ and $A \in B$, then why $x \notin B$?

Answer 1

Let $x=2$, $A= \{ 2 \}$, $B=\big\{ \{ 2 \} \big\}$. $B$ is a set with an element that is a set. $x$ isn't a set.

Answer 2

If $x \in A$ and $A \in B$, it doesn't imply that $x \in B$.

For example. Let $x=0, A=\{0\}$ and $B= \{ \{0\}\}$.

$\{0\}$ is an element of $B$ but $0$ is not an element of $B$.

Answer 3

Missouri is a member of the United States. The United States is a member of the United Nations. Missouri is not a member of the United Nations.