Answer: The running time should at least 119.32 seconds to be in the top 5% of runners.
Step-by-step explanation:
Let X= random variable that represents the running time of men between 18 and 30 years of age.
As per given, X is normally distrusted with mean and standard deviation
.
To find: x in top 5% i.e. we need to find x such that P(X<x)=95% or 0.95.
i.e.
Since, z-value for 0.95 p-value ( one-tailed) =1.645
So,
Hence, the running time should at least 119.32 seconds to be in the top 5% of runners.