math
posted by Antonee .
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

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.
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