For a die, the numbers that are odd are \( 1, 3, 5 \). The probability of rolling an odd number is:
\[
P(\text{odd}) = \frac{3}{6} = \frac{1}{2}.
\]
The probability of rolling an even number is also \( \frac{1}{2} \). Using the binomial probability formula, for exactly one odd number in three rolls:
\[
P(\text{one odd}) = \binom{3}{1} \left( \frac{1}{2} \right)^1 \left( \frac{1}{2} \right)^2 = 3 \cdot \frac{1}{8} = \frac{3}{8}.
\]