Question

in a group of student ,100 student know hindi,50 know english and 25 know both . each of the students know either hindi and english . How many students are there in the group?

Answer 1

Let H and E is the set of students who know Hindi and English respectively. 
n(H) = 100, n(E) = 50 and n(H ∩ E) = 25 
Use formula 
n ( H ∪ E ) = n (H ) + n ( E ) – n ( H ∩ E) 
Plug the values we get, 
= [100 + 50 - 25] 
⇒ 125 
Therefore, there are 125 students in the group. 

Answer 2

Total no. Of students = 100
Know hdi = 50
Know both = 25
Those know only hdi =50-25 = 25
So those who know English will be
25+25+x =100
X=50
So 50 know only English
Hope it was helpful