Scores made on a certain aptitude test by nursing students are approximately normally distributed with a mean of 500 points and a variance of 10,000. A random sample of the students is to be taken. How many students must be selected in the sample so that there is a 90% chance or better of at least one of them having a test score outside the range 304 to 696?

Now, I know the range of scores constitutes 97.5% of the area under the curve (the z value is 1.96). And that the probability that someone scores outside this range is 2.5%. But I am not sure how to find a sample size with a 90% chance of someone being outside the range

HELP!