Independent solution

How to solve this Counting Principles question

Setup

Setup

The three distinguishable dice generate 6 cubed equally likely ordered outcomes.

Nall=63=216N_{\mathrm{all}}=6^3=216

Model

Model

An outcome with exactly one pair is determined by its repeated value, its different value, and the location of the different value.

Npair=65(31)N_{\mathrm{pair}}=6\cdot5\cdot\binom31

Compute

Compute

Divide the favorable ordered outcomes by the complete sample space.

Pr(exactly one pair)=6(5)(3)216=90216=512=0.4166667\Pr(\text{exactly one pair})=\frac{6(5)(3)}{216}=\frac{90}{216}=\frac5{12}=0.4166667\ldots

Answer

Answer

The requested probability rounds to 0.417.

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