Kushan went to a bookseller's shop and purchased $2$ textbooks of Mathematics $IX$ and $3$ textbooks of Mathematics $X$ for Rs. $250$. His friend Rajan also bought $4$ textbooks of Mathematics $IX$ and $6$ textbooks of Mathematics $X$ of the same kind for Rs. $500$. Represent this situation as a pair of linear equations in two variables.

Let the cost of one textbook of Mathematics $IX$ be Rs. $x$ and the cost of one textbook of Mathematics $X$ be Rs. $y$.
Kushan purchased $2$ textbooks of Mathematics $IX$ and $3$ textbooks of Mathematics $X$. The total cost is represented by the expression $(2x + 3y)$.
Given that the total cost is Rs. $250$,we have:
$2x + 3y = 250$ ........ $(1)$
Rajan purchased $4$ textbooks of Mathematics $IX$ and $6$ textbooks of Mathematics $X$. The total cost is represented by the expression $(4x + 6y)$.
Given that the total cost is Rs. $500$,we have:
$4x + 6y = 500$ ........ $(2)$
Thus,the equations $(1)$ and $(2)$ represent the given situation as a pair of linear equations in two variables.