In a set of 400 ACT scores where the mean is 22 and the standard deviation is 4.5, how many scores are expected to be lower than 26.5?
How many of the 400 scores are expected to be greater than 31?
Z = (score-mean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z scores.
Multiply by 400.