**A physical-fitness association is including a mile run in its secondary-school fitness test for boys. The time for this event for boys in secondary school is approximately normally distributed with a mean of 450 seconds and a standard deviation of 40 seconds.**

a)What is the probability that a randomly selected boy takes between 420 and 540 seconds to run a mile?

solution: normalcdf(420,540,450,40) = .761 = 76.1%

b)What is the probability that a randomly selected boy takes at least 480 seconds to run a mile?

solution: normalcdf(480,E99,450,40) = .227 = 22.7%

c)What is the probability that a randomly selected boy takes at most 390 seconds to run a mile?

solution: normalcdf(E99,390,450,40) = .0668 = 6.68%

d)If the association wants to designate the fastest 20% as "above average, what time should the association set for this criterion?

solution: please give me advice!

e)If the association wants to designate the slowest 5% as "in need of medical evaluation," what time should the association set for this criterion?

solution: please give me advice!

Thank you in advance! I am trying!!