2006 #1 – The Catapults
Two parents have each built a toy catapult for use in a game at an
elementary school fair. To play the game, the students will
attempt to launch Ping-Pong balls from the catapults so that the
balls land within a 5-centimeter band. A target line will be drawn
through the middle of the band, as shown in the figure below. All
points on the target line are equidistant from the launching
location. If a ball lands within the shaded band, the student will
win a prize.
2006 #1 – The Catapults
The parents have constructed the two catapults according to
slightly different plans. They want to test these catapults before
building additional ones. Under identical conditions, the parents
launch 40 Ping-Pong balls from each catapult and measure the
distance that the ball travels before landing. Distances to the
nearest centimeter are graphed in the dotplot below.
2006 #1 – The Catapults
a) Comment on any similarities and any differences in the two
distributions of distances traveled by balls launched from
catapult A and catapult B.
b) If the parents want to maximize the probability of having the
Ping-Pong balls land within the band, which one of the
catapults, A or B, would be better to use than the other?
Justify your choice.
c) Using the catapult that you chose in part (b), how many
centimeters from the target line should this catapult be
placed? Explain why you chose this distance.
2006 #2 – Soapsuds
A manufacturer of dish detergent believes the height of
soapsuds in the dishpan depends on the amount of detergent
used. A study of the suds’ height for a new dish detergent was
conducted. Seven pans of water were prepared. All pans were
of the same size and type and contained the same amount of
water. The temperature of the water was the same for each pan.
An amount of dish detergent was assigned at random to each
pan, and that amount of detergent was added to that pan. Then
the water in the dishpan was agitated for a set of amount of
time, and the height of the resulting suds were measured.
2006 #2 – Soapsuds
A plot of the data and
the computer printout
from fitting a leastsquares regression line
to the data are shown
below.
2006 #2 – Soapsuds
a)
Write the equation of the fitted regression line. Define any
variables used in this equation.
b)
Note that s = 1.99821 in the computer output. Interpret
this value in the context of the study.
c)
Identify and interpret the standard error of the slope.
2008B #4 – Music and Blood Pressure
A researcher wants to conduct a study to test whether listening
to soothing music for 20 minutes helps to reduce diastolic blood
pressure in patients with high blood pressure, compared to
simply sitting quietly in a noise-free environment for 20 minutes.
One hundred patients with high blood pressure at a large
medical clinic are available to participate in this study.
2008B #4 – Music and Blood Pressure
a)
Propose a design for this study to compare these two
treatments.
2008B #4 – Music and Blood Pressure
b)
The null hypothesis for this study is that there is no
difference in the mean reduction of diastolic blood pressure
for the two treatments and the alternative hypothesis is
that the mean reduction in diastolic blood pressure is
greater for the music treatment. lf the null hypothesis is
rejected, the clinic will offer this music therapy as a free
service to their patients with high blood pressure. Describe
Type I and Type II errors and the consequences of each in
the context of this study, and discuss which one you think is
more serious.
1997, FRQ#2 – Fish Tanks
APAI Math/Science Day 3 —
14
Probability Practice
All bags entering a research facility are screened.
Ninety-seven percent of the bags that contain
forbidden material trigger an alarm. Fifteen
percent of the bags that do not contain
forbidden material also trigger the alarm. If 1
out of every 1,000 bags entering the building
contains forbidden material, what is the
probability that a bag that triggers the alarm will
actually contain forbidden material?
Organize the Problem
• Label the Events
– F – Bag Contains Forbidden Material
– A – Bag Triggers an Alarm
• Determine the Given Probabilities
– P(A|F) = 0.97
– P(A|FC) = 0.15
– P(F) = 0.001
• Determine the Question
– P(F|A) ?
Set up a Tree Diagram
A
0.97
F
0.03
0.001
AC
Non-Conditional
Probabilities
A
0.999
0.15
FC
0.85
AC
Conditional
Probabilities
Calculate the Probability
• P(F|A)
= P(F and A) / P(A)
• P(A)
= P(F and A) or P(FC and A)
= .001(.97) + .999(.15)
.15082
• P(F and A) = .001(.97) = .00097

P(F|A) = .00097/.15082 = 0.006
=
2002 #3 - The Runners
There are 4 runners on the New High
School team. The team is planning to
participate in a race in which each
runner runs a mile. The team time is
the sum of the individual times for the
4 runners. Assume that the individual
times of the 4 runners are all
independent of each other. The
individual times, in minutes, of the
runners in similar races are
approximately normally distributed
with the following means and standard
deviations.
Runner Mean SD
1
4.9
0.15
2
4.7
0.16
3
4.5
0.14
4
4.8
0.15
2002 #3 - The Runners
a) Runner 3 thinks that he can run a
mile in less than 4.2 minutes in the
next race. Is this likely to happen?
Explain.
b) The distribution of possible team
times is approximately normal.
What are the mean and standard
deviation of this distribution?
c) Suppose the teams best time to
date is 18.4 minutes. What is the
probability that the team will beat
its own best time in the next race?
Runner Mean SD
1
4.9
0.15
2
4.7
0.16
3
4.5
0.14
4
4.8
0.15