A bag contains 4 white,5 red6 blue balls.3 balls are drawn randomly from a bag, the probability of getting all the three red is?

total number of balls = 4+5+6 = 15 balls
out of 15 balls , the number of ways of choosing 3 balls is equal to the number of sample space.
number of sample space = ${}^{15}C_3 =\frac{15*14*13}{3*2}=455$

the number of ways of choosing 3 red balls = ${}^{5}C_3 =\frac{5*4}{2}=10$

the probability of getting all the three red balls $=\frac{10}{455}=\frac{2}{91}$

hope this helps you