probablity

[eco201611]

An entrance examination has 10 \true-false" questions. A student an-
swers all the questions randomly and his probability of choosing the
correct answer is 0:5. Each correct answer fetches a score of 1 to the
student, while each incorrect answer fetches a score of zero. What is
the probability that the student gets the mean score?

[Dr. Strange]

Mean score =5
P(MEAN score=5)=P(no. of right answers=5)= C(10,5)*(1/2)^5 * (1/2)^5
=63/256