Independent solution

How to solve this Hypergeometric Distribution question

Setup

Setup

Treat the inspection as a sample without replacement from seven intact and three damaged boxes.

Nall=(105)N_{\mathrm{all}}=\binom{10}{5}

Model

Model

Exactly three intact boxes requires choosing the remaining two boxes from the damaged group.

Nfav=(73)(32)N_{\mathrm{fav}}=\binom73\binom32

Compute

Compute

Evaluate the hypergeometric ratio.

Pr(X=3)=(73)(32)(105)\Pr(X=3)=\frac{\binom73\binom32}{\binom{10}{5}}
=353252=512=0.416666=\frac{35\cdot3}{252}=\frac5{12}=0.416666\ldots

Answer

Answer

The probability of finding exactly three intact boxes is approximately 0.417.

0.417(D)\boxed{0.417\quad\text{(D)}}