math
posted by Matt .
The FunTime Amusement park customer load during the summer follows a normal distribution with mean 450 and standard deviation 80. Determine the probability that the number of customers on any given day during the summer will be less than 420.

Z = (x  μ)/SD
Plug in the values and find Z score in table in the back of your stats book labeled something like "areas under the normal distribution." Since the score is less than the mean, lower scores will be in the smaller portion.
I hope this helps. Thanks for asking.