Concept:
Probability = $\frac{\text{Favourable outcomes}}{\text{Total outcomes}}$
Explanation:
A standard deck has 52 cards.
Face cards: Jack, Queen, King in each of 4 suits.
Total face cards:
\[
3 \times 4 = 12
\]
Probability:
\[
\frac{12}{52} = \frac{3}{13}
\]