Correct Answer - A
Let n and p be the parameters for the distribution.
We have,
Mean =4 and Variance =2
⇒np=4andnpq=2⇒p=q=
1
2
andn=8
Let X denote the number of successes. Then,
P(X=r)=.8Cr(
1
2
)r(
1
2
)8-1=.8Cr(
1
2
)8
∴ Required Probability =P(X=2)=.8C2(
1
2
)8=
28
256
