a person received a test score that was in the top 20% of everyone who has taken the test. the test scores are normally distributed. this perosn's Z score must be at least what/
Use your table of z-scores. The top 20% will be the bottom 50%, plus another 30%, so find the z-score corresponding to 0.3000, or as close as you can get. You should arrive at a value in the vicinity of 0.8415.