Question

1. A group consists of one hundred and forty students. Of these, eighty are studying Norwegian, forty are studying Swedish and fifteen are studying Norwegian and Swedish. A student is selected at random. What is the probability that a student is studying Norwegian or Swedish?

Answer 1

$n(A\bigcap B)=n(A)+n(B)-n(A\bigcup B)$

By using above formulae

n(A)=80

n(B)=40

$n(A\bigcap B)$ =15

so we apply above formulae

15=80+40- $n(A \bigcup B)$

$n(A \bigcup B)$ =80+40-15

=105

so answer is 105