Problem 11 - Entrance Test

A die is rolled 4 times. What is the probability of exactly two 6's?

A. C(4,2)·5^2/6^4B. C(4,2)/6^2C. 25/6^4D. C(4,2)·25/6^4

Correct: D

Binomial: n=4, k=2, p=1/6. P=C(4,2)(1/6)^2(5/6)^2=C(4,2)·25/6^4.