#### Transcript 2.5 Day 2

```Warm-up 2.5 Day 2
1)An incoming freshman took her college’s placement exams
in French and mathematics. In French, she scored 82 and in
math, 86. The overall results on the French exam had a
mean of 72 and a standard deviation of 8, while the mean
math score was 68 with a standard deviation of 12. On
which exam did she do better compared with the other
freshmen?
Warm-up Day 2
2) Two companies market new batteries targeted at owners of
personal music players. DuraTunes claims a mean battery life of 11
a) Explain why you would also like to know the standard
deviations of the battery lifespans before deciding which brand to
b) Suppose those standard deviations are 2 hours for DuraTunes
and 1.5 hours for RockReady. You are headed for 8 hours at the
beach. Which battery is most likely to last all day? Explain.
c) If your beach trip is all weekend, and you probably will havethe
music on for 16 hours, which battery is most likely to last? Explain.
Mooseburger vs.McTofu
3)M-burgers’s weekly payroll number are mostly higher
than McTofu. McTofu has an outlier that is out of place.
McTofu vs. Mooseburger
4) On average Mooseburger pays the higher
salaries.
5) The mean salary is misleading for McTofu
because it has an outlier which will make the mean
payroll considerably higher.
6) Mooseburger has consistently higher payrolls,
McTofu has one high payroll number which may be
a manager. This McTofu’s numbers misleading.
Student of the Day!
Block 4
Student of the Day!
Block 5
Student of the Day!
Block 6
Z-score
Z-scores (for normal distribution) describe how many
standard deviations (σ) a piece of data is from the
x  
mean(μ).
z 

The z-score can also be used to find the proportion of
values above or below the z-score using
normalcdf (z-score, upper or lower bound)
invNorm is for finding the z-score when the percentile, mean
and standard deviation is given.
invNorm(percentile,mean, standard deviation)
Practice with z-scores and finding proportions.
1) A distribution of quiz scores has a mean of 35 and
an standard deviations of of 4. Sara received a 40.
a) What is her z-score?
b) What is her percentile rank compared to the rest
of the class?
2) In a normal distribution with mean 25 and standard
deviation 7, what proportion of the data are less than 20?
Multiple Choice Practice
• Answer 1 – 10 by yourself.
• Once everyone at your table is done, discuss your