Using the normal curve table for this problem. If a person received a test score that was in the top 20% of everyone who has taken the test and the test scores are normally distributed. This person's Z score must be at least:

What's your emperical rule? One standard deviation is 34%-ish. Z = 1, then, would represent about 84%. That's too big. This discards two of the choices. What say you of the other two?