Question

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

Answer 1

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 = (score-mean)/SD

Insert the values to solve for both +Z and -Z.