Mathematics 9709 · AS & A Level · Continuous random variables

Continuous random variables — practice question

Let $X$ be distributed as $N(-3,\sigma^2)$. The chance that a value of $X$ selected at random is greater than 0 is $0.25$.

(i)[3]

Determine the value of $\sigma$.

(ii)[3]

Determine the probability that, among $8$ random values of $X$, fewer than $2$ are positive.

Worked solution & mark scheme

This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “The value $z = \pm 0.674$ is stated or inferred.” …