Question

A bag contains 3 red, 7 white and 4 black balls. If three balls are drawn from the bag, then the probability that all of them are of the same colour is

• A. $\frac { 6 } { 71 }$
• B. $\frac { 7 } { 81 }$
• C. $\frac { 10 } { 91 }$
• D. None of these

Answer 1

Answer: (C)

$\frac { 10 } { 91 }$

Answer 2

Required probability $= \frac { { } ^ { 3 } C _ { 3 } + { } ^ { 7 } C _ { 3 } + { } ^ { 4 } C _ { 3 } } { { } ^ { 14 } C _ { 3 } }$

$= \frac { 1 + 35 + 4 } { 14.13 .2 } = \frac { 40 } { 14.26 } = \frac { 10 } { 91 }$