An urn contains 5 white, 6 red and 4 blue balls. Three balls are...

Total number of balls in the urn = $5 + 6 + 4 = 15$

Total number of ways to draw 3 balls from 15 balls = ^{15}C_{3} = $\dfrac{15 \times 14 \times 13}{3 \times 2 \times 1} =455$

Number of ways to draw 1 white, 1 red and 1 blue ball = ^{5}C_{1} \times ^{6}C_{1} \times ^{4}C_{1} = 5 \times 6 \times 4 = 120$<br><br>Required probability = \dfrac{120}{455} = \dfrac{24}{91}$