Mathematics 9709 · AS & A Level · Sampling and estimation

Sampling and estimation — practice question

A group of $4$ is chosen at random from $3$ boys and $5$ girls. Let the random variable $X$ denote the number of girls in the group.

(i)[4]

Construct a probability distribution table for $X$.

(ii)[2]

Using $\mathrm{E}(X)=\frac{5}{2}$, calculate $\mathrm{Var}(X)$.

Worked solution & mark scheme

This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Take $X=1,2,3,4$ as the possible values.” …