In a certain code language,
* '$A+B$ ' means 'A is the father of B',
* '$A-B$ ' means 'A is the husband of B',
* '$A\times B$ ' means 'A is the mother of B',
* '$A÷B$ ' means 'A is the brother of B'.

How is P related to T if the expression is '$P+Q-R\times S÷T$ '?

Let's decode the given expression step-by-step from left to right:
1. $P+Q\to$ P is the father of Q. (P is male).
2. $Q-R\to$ Q is the husband of R. (Q is male, R is female).
3. $R\times S\to$ R is the mother of S. Since Q is R's husband, Q is the father of S.
4. $S÷T\to$ S is the brother of T. This means S and T are siblings sharing the same parents (Q and R).

From steps 3 and 4, Q is the father of T.
From step 1, P is the father of Q.
Therefore, P is the father of T's father, which means P is T's father's father (paternal grandfather).