If the total distance run by the 3 members of the relay team is \( \frac{3}{8} \) of a mile and each runner ran the same distance, we can find out how far each person ran by dividing the total distance by the number of runners.
So we calculate:
\[ \text{Distance per runner} = \frac{\text{Total distance}}{\text{Number of runners}} = \frac{\frac{3}{8}}{3} \]
To divide \( \frac{3}{8} \) by 3, we can multiply by the reciprocal of 3:
\[ \frac{3}{8} \div 3 = \frac{3}{8} \times \frac{1}{3} = \frac{3 \times 1}{8 \times 3} = \frac{3}{24} = \frac{1}{8} \]
Therefore, each person ran \( \frac{1}{8} \) of a mile.
The answer is \( \frac{1}{8} \) of a mile.