Probability of drawing yellow and black balls

Total balls = $8 + 4 = 12$. Total ways to choose 3 balls = $\binom{12}{3} = \frac{12 \times 11 \times 10}{6} = 220$. Favorable ways = $\binom{8}{2} \times \binom{4}{1} = 28 \times 4 = 112$. Probability = $\frac{112}{220} = \frac{28}{55}$.