or lower on a 100question test. (Round
your answer to four decimal places.)
(b) If the test contains 250 questions, what is the probability that Jodi will score
72%
or lower? (Use the normal
approximation. Round your answer to four decimal places.)
(c) How many questions must the test contain in order to reduce the standard deviation of Jodi's proportion of correct
answers to half its value for a 100item test?
questions
(d) Laura is a weaker student for whom
p
=
0.71
. Does the answer you gave in (c) for standard deviation of Jodi's score
apply to Laura's standard deviation also?
9/11/2018
Topic Three Homework Revak
13.
–/1.053 pointsMIntroStat9 5.E.094.
Does delaying oral practice hinder learning a foreign language? Researchers randomly assigned
17
beginning students of Russian
to begin speaking practice immediately and another
17
to delay speaking for 4 weeks. At the end of the semester both groups
took a standard test of comprehension of spoken Russian. Suppose that in the population of all beginning students, the test
scores for early speaking vary according to the
N
(
29
,
4
) distribution and scores for delayed speaking have the
N
(
24
,
distribution.
(a) What is the sampling distribution of the mean score
x
in the early speaking group in many repetitions of the
experiment? (Round your answers for
s
to two decimal places.)
3
)
8/11
(c) What is the probability that the experiment will find (misleadingly) that the mean score for delayed speaking is at
least as large as that for early speaking? (Round your answer to four decimal places.)
What is the sampling distribution of the mean score
y
in the delayed speaking group?
(b) If the experiment were repeated many times, what would be the sampling distribution of the difference
y

between the mean scores in the two groups? (Round your answer for
s
to two decimal places.)
x
9/11/2018
Topic Three Homework Revak
9/11
14.
–/1.053 pointsMIntroStat9 5.E.059.
In each of the following situations, is it reasonable to use a binomial distribution for the random variable
X
? Give reasons for your
answer in each case. If a binomial distribution applies, give the values of
n
and
p
(a)
A poll of 200 college students asks whether or not you usually feel irritable in the morning.
X
is the number who reply that
they do usually feel irritable in the morning.
Yes, a binomial distribution is reasonable;
B
(
p
, 200).
Yes, a binomial distribution is reasonable;
B
(200, 1/2).
Yes, a binomial distribution is reasonable;
B
(200,
p
Yes, a binomial distribution is reasonable;
B
(1/2, 200).
No, a binomial distribution is not reasonable.
.
).