In a group of 65 people, 40 like cricket, 10 like both cricket and tennis. How many like tennis only and not cricket?

Let C denote the set the people like cricket, and T denote the set of people who like tennis
∴n(C∪T)=65,n(C)=40,n(C∩T)=10
We know that
n(C∪T)=n(C)+n(T)−n(C∩T)
∴65=40+n(T)−10
∴65=30+n(T)
∴n(T)=65−30=35
Therefore, 35 people like tennis.
Now,
n(T−C)=n(T)−n(T∩C)
∴n(T−C)=35−10=25
Thus, 25 people like only tennis.