Question

Elaine is taking a test that has multiple choice questions,each with 4 answer choices. She comes to a question for which she does not know the awnser. If she can rule out three of the choices as wrong, by how much does she improve her probability of guessing correct awnser?

Answer 1

Assuming There is ONLY ONE CORRECT ANSWER,

The probability of her guessing the answer without ruling out the choices is 1/5.

if 3 choices are ruled out, then 1 out of the remaining two is right, which gives the probability 1/2

now, 1/5 = 20% , while 1/2 = 50%.

Therefore her probability of getting the correct answer improves by 30% [ not much in a REAL test though :P ]