In Example 2, what percentage of the test scores are between 350 and 650?

Data from Example 2

The scores on a certain achievement test are normally distributed with a mean of 500 and a standard deviation of 50. What percentage of the scores are (a) between 400 and 600, and (b) higher than 550?
(a) Since 400 is two standard deviations below the mean and 600 is two standard deviations above the mean, about 95% of all scores are between these values.
(b) The value 550 is one standard deviation above the mean. This means that about 34% (half of 68%) of the scores are between 500 and 550. Therefore, the percentage of scores that are higher than 550 is about 16%(50% − 34%). [Remember that the total area under any normal curve is 1(or100%). Because a normal curve is symmetric, the area on either side of the mean is 0.5(or50%).]