Posted by Antonee on .
the mean life of a tire is 30,000 km. the standard deviation is 2000 km. 68% of all tires will have a life between _km and _ km

math 
PsyDAG,
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (.34) from the mean for a Z score.
Z = (scoremean)/SD
Insert the values to solve for both +Z and Z.