This preview shows pages 1–2. Sign up to view the full content.
ACTIVITY 6
 Solutions
Activity 6.1
Suppose the amount students at PSU spent on textbooks this semester is a normal random
variable with mean μ= $360 and standard deviation σ = $90.
a.
Use the empirical rule for bellshaped data to determine intervals that will contain about 68%,
95% and 99.7% of amounts spent on textbooks by PSU students. Show work for each interval.
68% will be in interval 360± 90, or $270 to $450
95% will be in interval 360± (2×90), or $180 to $540
99.7% will be in interval 360± (3×90), or $90 to $630
b.
With Minitab, find the cumulative probability for $300. Use
Calc>Probability
Distributions>Normal
, enter the mean and standard deviation, click on “Input Constant” and
enter 300 in the adjacent box. [Note: The notation for the probability you’re finding is P(X ≤
$300).]
x
P( X <= x )
300
0.252493
c.
Write a sentence interpreting the value found in the previous part that would be understood by
somebody with no training in statistics.
About 25% of PSU students spent less than $300 on textbooks this semester.
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
This is the end of the preview. Sign up
to
access the rest of the document.
 '08
 BARROSO,JOAOR
 Statistics, Empirical Rule, Standard Deviation

Click to edit the document details