3.25 Standard Normal drill.

(a) Find the number z such that the proportion of observa tions that are less than ?: in a standard Normal distribution is 0.8.

(b) Find the number ? such that 35% of all observations from a standard Normal distribution are greater than z-
3.26 Running a mile. After the physical training required during World War 11, the distribution of mile run times for male students at the University of Illinois was approximately Normal with mean 7.11 minutes and staiadard deviation 0.74 minute.
What proportion of these students could run a mile in 5 min utes or less?