Correct Answer - C
It is a problem on binomial distribution in which n=5,p=
probability that the answer of a question is correct =
1
3
andq=1-
1
3
=
2
3
. Let X denote the number of correct answer. Then,
P(X=r)=.5Cr(
1
3
)r(
2
3
)5-r,r=0,1,2,....,5
Required Probability =P(X≥4)=P(X=4)+P(X=5)
=.5C4(
1
3
)4(
2
3
)1+.5C5(
1
3
)5(
2
3
)0=
10
35
+
1
35
=
11
35
