Question

There are 20 teachers 12 teach accountancy 4 teach statistics and accountancy so how many teach Statistics

Answer 1

hello users ....
solution:-
let n(A) denotes teacher teach Accountancy. 
And
also n(B) denotes teacher teach statistics . 

here,
total no. of teacher = n(A∪B) = 20
and
Number of teacher teach Accountancy n(A) = 12 
And
number of teacher teaches both Accountancy and statistics
= n (A∩B)  = 4

we have to find :
number of teacher teach statistics = n(B) = ?

Here,
we know that 
n(A∪B) = n(A) + n(B) - n(A∩B)
=>n(B) =  n(A∩B) + n(A∪B) - n(A)

=> n(B) = 4 + 20 -12 

=> n(B) = 12

=> The number of teacher teach statistics = 12 Answer 

@ hope it helps :)