Question

The probability of choosing a quarterback from the football team is 1/15. The probability of choosing a quarterback and pitcher is 1/315. What is the probability of choosing a pitcher?

Answer 1

Assuming the choice of either quarterback $(Q)$ or pitcher $(P)$ is independent of one another, you have

$\mathbb P(Q\cap P)=\mathbb P(Q)\mathbb P(P)$
$\dfrac1{315}=\dfrac{\mathbb P(P)}{15}$
$\implies\mathbb P(P)=\dfrac{15}{315}=\dfrac1{21}$