You need to take Chebyshev's Theorem, and figure out between what 2 scores you would find 160/200 (80%) of the patients
i.e., 1 - (1/k^2) = 80% --> solve for k, and this will be the number of standard deviations
Use the Empirical Rule (i.e., 68% within +/- 1 std dev, 95% within +/-2, etc.) to determine the % of patients' scores between the given boundaries
i.e., how many standard deviations from the mean is the 5th percentile, how many st dev from the mean is a score of 97?
use the formula z = (x - mu)/s