Posted by Pat on .
The time it takes Jessica to bicycle to school is normally distributed with an average of a third of an hour and a variance of 9 minutes. Jessica has to be at school at 8:15 am. What time should she leave the house so she will be late on 5% of the time?

statistics 
PsyDAG,
Z = (scoremean)/SD
1/3 hour = 20 minutes
Variance = SD^2
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion .05 and insert its Z score in the equation above with the other data. Find difference from 8:15.