Solution:

Let’s suppose that,

The set of all students in the group be U

The set of students who know English be E

$\therefore \mathrm{H} \cup \mathrm{E}=\mathrm{U}$

Provided that,

$n(H)=100$ = Number of students who know Hindi

$n(E)=50$ = Number of students who knew English,

$n(H \cap E)=25$ = Number of students who know both,

We need to find the total number of students in the group i.e. $n(U)$

$\therefore$ As per the question,

$n\text{ }\left( U \right)\text{ }=\text{ }n\left( H \right)\text{ }+\text{ }n\left( E \right)-n(H\cap E)$

$=\text{ }100\text{ }+\text{ }50-25$

$= 125$

$\therefore$ $125$ is the total number of students in the group students.