Question

A bag contains 3W and 2B balls. Two balls are drawn at

random and white ball is considered as success. Then the

mean of the probability distribution for the number of successes X is

• A. 9/25
• B. 6/5
• C. 9/5
• D. 9/5

Answer 1

Answer: (B)

6/5

Answer 2

X = {0, 1, 2}

P(x=0) = $\frac { { } ^ { 2 } \mathrm { C } _ { 2 } } { { } ^ { \mathrm { r } } \mathrm { C } _ { 2 } } = \frac { 1 } { 10 }$ P(x=1) = $\frac { { } ^ { 2 } \mathrm { C } _ { 1 } { } ^ { 3 } \mathrm { C } _ { 1 } } { { } ^ { \mathrm { r } } \mathrm { C } _ { 2 } } = \frac { 6 } { 10 }$

P(x=2) = $\frac { { } ^ { 3 } \mathrm { C } _ { 2 } } { { } ^ { 5 } \mathrm { C } _ { 2 } } = \frac { 3 } { 10 }$

Probability distribution table is

X	0	1	2
P(x)	1/1 0	6/10	3/10

Mean X = $\frac { 6 } { 10 } + \frac { 6 } { 10 } = \frac { 12 } { 10 } = \frac { 6 } { 5 }$