The time that it takes a randomly selected job applicant to

The time that it takes a randomly selected job applicant to perform a certain task has a distribution that can be approximated by a normal distribution with a mean value of 125 sec and a standard deviation of 25 sec. The fastest 10% are to be given advanced training. What task times qualify individuals for such training? (Round the answer to one decimal place.)
seconds or less

Solution

Normal Distribution
Mean ( u ) =125
Standard Deviation ( sd )=10
Normal Distribution = Z= X- u / sd ~ N(0,1)                  
P ( Z > x ) = 0.1
Value of z to the cumulative probability of 0.1 from normal table is 1.28
P( x-u/ (s.d) > x - 125/10) = 0.1
That is, ( x - 125/10) = 1.28
--> x = 1.28 * 10+125 = 137.82  
times qualify individuals for such training is ~ 137.8