CHEMISTRY 31

Summer, 2016 - Dixon

Homework Set 1 – Additional Problem 1.3

Solutions

3.  A certain 100 point quantitative analysis exam has an average value of 64.2 and a standard deviation of 19.0.  If the cut-off limit for an "A" is 87, determine what percentage of students should be getting an A.  Assume the distribution of test scores is Gaussian, and use the Z-Table below - find the closest Z value; do not interpolate.

Z = (87 – 64.2)/19.0 = 1.20

Area given from table is Z between 0 and 1.2 = 0.385

Area for Z > 1.2 = 0.5 – 0.385 = 0.115 or 11.5%

The subtraction is done because we want the fraction of students above 87 and 0.5 corresponds to half of the students having scores above the mean.