Question

Q and R are not mutually exclusive events. p (q) = 3/5 p(r) = 1/3 and p ( q and r)= 1/5 find P(Q or R).

Answer 1

Recall the inclusion/exclusion principle:

$\mathbb P(Q\cup R)=\mathbb P(Q)+\mathbb P(R)-\mathbb P(Q\cap R)$

which means

$\mathbb P(Q\text{ or }R)=\dfrac35+\dfrac13-\dfrac15=\dfrac{11}{15}$