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 ]
It the property of distributive
Answer: The answer is 315.
