10. A bag contains 2 red balls, 3 white balls, and 4 yellow balls. If 4 balls are drawn at random, the probability that all three colors are included is $\qquad$ .
Let $A=$ "all three colors of balls are present", then $P(A)=\frac{C_{2}^{2} \cdot 3 \cdot 4+C_{3}^{2} \cdot 2 \cdot 4+C_{4}^{2} \cdot 2 \cdot 3}{C_{9}^{4}}=\frac{12+24+36}{126}=\frac{4}{7}$.