What is the probability of guessing correctly at least 8 out of 10 answer on true-false examination?

Explanation

`p(Xge8)`
`=""^(10)C_(8)((1)/(2))^(8)((1)/(2))^(2)+""^(10)C_(9)((1)/(2))^(9)((1)/(2))^(1)+""^(10)C_(10)((1)/(2))^(10)`
`=((1)/(2))^(10)[""^(10)C_(2)+""^(10)C_(0)]`
`=((1)/(2))^(10)[45+41+1]`
`(56)/(8xx2^(7))=7/128`