Question

What is the probability of getting 80% or more of the questions correct on a 10-question true-false exam merely by guessing?

Answer 1

Binomial distribution with p = .5

p(10 right)
= c(10,10) .5^10 (.5)^0 =.5^10 = .000976

p( 9 right)
= c(10,9) .5^9 (.5)^1 = .00976

p(8 right)
= c(10,8) (.5)^8 (.5)^2 = 45*.5^10 = .04394

sum = .0547

Answer 2

I can't understand your way.... can u explain or do it another way