5. A fair coin is flipped 9 times. What is the probability of getting exactly 6 heads?
11. A group of students at a school takes a history test. The distribution is normal
with a mean of 25, and a standard deviation of 4. (a) Everyone who scores in
the top 30% of the distribution gets a certificate. What is the lowest score
someone can get and still earn a certificate? (b) The top 5% of the scores get to
compete in a statewide history contest. What is the lowest score someone can
get and still go onto compete with the rest of the state?
12. A person claims to be able to predict the outcome of flipping a coin. This
person is correct 16/25 times. Compute the 95% confidence interval on the
proportion of times this person can predict coin flips correctly. What
conclusion can you draw about this test of his ability to predict the future?
112. Table 3.22 identifies a group of children by one of four hair colors, and by type of hair.
Hair Type Brown Blond Black Red Totals
a. Complete the table.
b. What is the probability that a randomly selected child will have wavy hair?
c. What is the probability that a randomly selected child will have either brown or blond hair?
d. What is the probability that a randomly selected child will have wavy brown hair?
e. What is the probability that a randomly selected child will have red hair, given that he or she has straight hair?
f. If B is the event of a child having brown hair, find the probability of the complement of B.
g. In words, what does the complement of B represent?
72. You buy a lottery ticket to a lottery that costs $10 per ticket. There are only 100 tickets available to be sold in this lottery. In this lottery there are one $500 prize, two $100 prizes, and four $25 prizes. Find your expected gain or loss.
76. Suppose that the distance of fly balls hit to the outfield (in baseball) is normally distributed with a mean of 250 feet and
a standard deviation of 50 feet.
a. If X = distance in feet for a fly ball, then X ~ _____(_____,_____)
b. If one fly ball is randomly chosen from this distribution, what is the probability that this ball traveled fewer than
220 feet? Sketch the graph. Scale the horizontal axis X. Shade the region corresponding to the probability. Find the probability.
c. Find the 80th percentile of the distribution of fly balls. Sketch the graph, and write the probability statement.
106. Suppose that a committee is studying whether or not there is waste of time in our judicial system. It is interested in the mean amount of time individuals waste at the courthouse waiting to be called for jury duty. The committee randomly surveyed 81 people who recently served as jurors. The sample mean wait time was eight hours with a sample standard deviation of four hours.
i. x ¯ = __________
ii. sx = __________
iii. n = __________
iv. n – 1 = __________
b. Define the random variables X and X ¯ in words.
c. Which distribution should you use for this problem? Explain your choice.
d. Construct a 95% confidence interval for the population mean time wasted.
i. State the confidence interval.
ii. Sketch the graph.
iii. Calculate the error bound.
e. Explain in a complete sentence what the confidence interval means.