In a class of $40$ students, $15$ students play cricket and $15$ students play tennis, and $5$ students play both the games. Then the number of students who play neither of the two games is :

Let's solve this using Set Theory rules:
* Total number of students, $n(U)=40$
* Students playing cricket, $n(C)=15$
* Students playing tennis, $n(T)=15$
* Students playing both games, $n(C\cap T)=5$

**Step 1: Find the total number of students who play at least one game ($n(C\cup T)$)**

$$n(C\cup T)=n(C)+n(T)-n(C\cap T)$$

$$n(C\cup T)=15+15-5=30-5=25$$

Step 2: Find the number of students who play neither game

$$\text{Neither Game}=n(U)-n(C\cup T)$$

$$\text{Neither Game}=40-25=15$$