statistik
posted by mira .
can you show me the calculation ;)
The life expectancy of computer terminals is normally distributed with a mean of 4 years and standard deviation for 10 months.
a. What is the probability that a randomly selected terminal will last more than 5 years?
b. What percentage of terminals will last between 2.5 years and 4.5 years?
c. 80 percent of terminals will last at least how many years?

Convert all values either into months or years.
Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions related to the Z scores. To get percentages, multiply by 100.
c. Reverse process to find Z score and calculate. 
0.102