Slide 1

• A study involving stress is done on a college campus
among the students. The stress scores are known to
follow a uniform distribution with the lowest stress
score equal to 1 and the highest equal to 5. A sample of
75 students is randomly chosen.
Let X = the stress score of one student.
Let = the average stress score of 75 students.
• X ~ U(1, 5)
•

mean = 3

 1.1547 
X ~ N  3,

75 


stdev = 1.1547


Slide 2

•Find the probability that the average stress score for
the 75 students is less than 2.

Probability Statement: P(X-bar < 2) = 0.0000
Calculator steps:
2nd,DISTR,normalcdf(-1E99,2,3,1.1547/sqrt(75)),Enter


Slide 3

•Find the 90th percentile for the AVERAGE stress
score for the 75 students. 90% of the average stress
scores are less than this value. Let k = the 90th %ile
Probability Statement: P(X-bar < k) = 0.90
k = 3.17
Calculator steps to find k:
2nd,DISTR,invNorm(0.9,3,1.1547/sqrt(75)),Enter