Question

In a group of 1000 people three are 750 who can speak Hindi and 400 who can speak Bengali. How many can speak both Hindi and Bengali ?

Answer 1

Both Hindi and Bengali
$n(H\cup B)=1000,n\left(H\right)=750,n\left(B\right)=400$
$n(H\cup B)=n\left(H\right)+n\left(B\right)-n(H\cap B)$
$\therefore 1000-750+400-n(H\cap B)$
$n(H\cap B)=150$