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Continue to assume that people are equally likely to be born during any of the months. However, just for the sake of this exercise, assume that there is a tendency for married couples to have been born during the same month. Furthermore, we wish to calculate the probability of a husband and wife both being born during December. (a) It would be appropriate to use the multiplication rule for independent outcomes. True or False? (b) The probability of a married couple both being born during December is smaller than, equal to, or larger than \((1 / 12)(1 / 12)=1 / 144 .\) (c) With only the previous information, it would be possible to calculate the actual probability of a married couple both being born during December. True or False?

Short Answer

Expert verified
(a) False. (b) Larger than \( \frac{1}{144} \). (c) False

Step by step solution

01

Understand the Multiplication Rule for Independent Outcomes

The multiplication rule for independent outcomes states that if two events are independent, the probability of both occurring is the product of the probabilities of each event occurring separately. Here, we can't use this rule because the problem assumes that the birth months of married couples are not independent events i.e., they have a tendency to coincide.
02

Comparing the Probability

The number \( \frac{1}{144} \) is calculated using the multiplication rule for independent outcomes. \( P(\text{{both in December}})=P(\text{{one person in December}}) \times P(\text{{other person in December}}) = \frac{1}{12} \times \frac{1}{12} = \frac{1}{144} \). Since we've established that these events are not independent, the actual probability should be higher, meaning that the probability of a married couple both being born during December is larger than \( \frac{1}{144} \).
03

Possibility of Calculating the Actual Probability

We cannot calculate the exact probability of a married couple being born in December with the given information. We're given only the likelihood that these events occur together more frequently than if they were independent, but without specific numbers or distributions, this information is not sufficient to calculate a precise probability.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Multiplication Rule for Independent Outcomes
The multiplication rule for independent outcomes is a fundamental concept in probability theory. It says that if you have two independent events—events whose occurrence does not affect each other—the probability of both events happening can be found by multiplying their individual probabilities.

For instance, consider rolling two dice. The probability of rolling a four on one die does not affect the probability of rolling a two on the other. If you want to find the probability of rolling a four and a two simultaneously, you calculate \(\frac{1}{6} \times \frac{1}{6} = \frac{1}{36}\), because each die has 6 outcomes and each outcome is equally likely.In the context of our exercise, we're presented with the scenario of married couples' birth months. If being born in December was truly independent for husband and wife, then you would calculate the probability by multiplying the chance of one being born in December \(\frac{1}{12}\) with the probability of the other being born in December \(\frac{1}{12}\), resulting in \(\frac{1}{12} \times \frac{1}{12} = \frac{1}{144}\). However, since the exercise states that married couples have a higher tendency to be born in the same month, the events are not independent. This means that different principles need to be applied, and we cannot use the multiplication rule for independent outcomes in this case.
Probability Comparison
Comparing probabilities involves determining whether one event is more or less likely than another, or if they're equally likely to occur. This kind of comparison is crucial in understanding the likelihood of different scenarios and making decisions based on probabilities.In our given problem, if the birth months were independent events, the calculated probability would be \(\frac{1}{144}\). However, since the exercise implies that there's a higher likelihood for married couples to share the same birth month, the actual probability would be larger than \(\frac{1}{144}\).

Imagine flipping two coins. The probability of getting heads on both is \(\frac{1}{4}\), as each coin has a 1 in 2 chance of landing on heads. If we had a rigged scenario where the coins were weighted to favor heads, the probability of getting two heads would be higher than \(\frac{1}{4}\), just as the probability of a married couple both being born in December is higher than \(\frac{1}{144}\) due to the stated tendency. This demonstrates the importance of understanding underlying relationships and dependencies in probability comparison.
Birth Month Coincidence
Birth month coincidence refers to the situation where two or more individuals have the same birth month. It can be interesting to calculate the probability of such occurrences, especially in the context of married couples as in our exercise.

Suppose we selected two random people. If the probability of each being born in any specific month (like December) is \(\frac{1}{12}\), and we treated their birth months as independent events, we'd conclude the chance of them sharing a birth month to be \(\frac{1}{144}\). However, human relationships and behaviors often involve patterns and tendencies, which can affect such probabilities. In real-life scenarios, like that of married couples, there could be social or psychological factors that may make the share of birth month not just a simple matter of chance. These scenarios create a deviation from the straightforward calculations made by assuming independent events.Understanding birth month coincidences involves not only a mastery of probability concepts but also an appreciation for the complexity of human behavior and social patterns, which can render seemingly unrelated events non-independent.

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Most popular questions from this chapter

Assume that the probability of breast cancer equals .01 for women in the \(50-59\) age group. Furthermore, if a woman does have breast cancer, the probability of a true positive mammogram (correct detection of breast cancer) equals .80 and the probability of a false negative mammogram (a miss) equals .20. On the other hand, if a woman does not have breast cancer, the probability of a true negative mammogram (correct nondetection) equals .90 and the probability of a false positive mammogram (a false alarm) equals .10. (Hint: Use a frequency analysis to answer questions. To facilitate checking your answers with those in the book, begin with a total of 1,000 women, then branch into the number of women who do or do not have breast cancer, and finally, under each of these numbers, branch into the number of women with positive and negative mammograms.) (a) What is the probability that a randomly selected woman will have a positive mammogram? (b) What is the probability of having breast cancer, given a positive mammogram? (c) What is the probability of not having breast cancer, given a negative mammogram?

A sensor is used to monitor the performance of a nuclear reactor. The sensor accurately reflects the state of the reactor with a probability of .97. But with a probability of .02, it gives a false alarm (by reporting excessive radiation even though the reactor is performing normally), and with a probability of .01 , it misses excessive radiation (by failing to report excessive radiation even though the reactor is performing abnormally). (a) What is the probability that a sensor will give an incorrect report, that is, either a false alarm or a miss? (b) To reduce costly shutdowns caused by false alarms, management introduces a second completely independent sensor, and the reactor is shut down only when both sensors report excessive radiation. (According to this perspective, solitary reports of excessive radiation should be viewed as false alarms and ignored, since both sensors provide accurate information much of the time.) What is the new probability that the reactor will be shut down because of simultaneous false alarms by both the first and second sensors? (c) Being more concerned about failures to detect excessive radiation, someone who lives near the nuclear reactor proposes an entirely different strategy: Shut down the reactor whenever either sensor reports excessive radiation. (According to this point of view, even a solitary report of excessive radiation should trigger a shutdown, since a failure to detect excessive radiation is potentially catastrophic.) If this policy were adopted, what is the new probability that excessive radiation will be missed simultaneously by both the first and second sensors?

Among 100 couples who had undergone marital counseling, 60 couples described their relationships as improved, and among this latter group, 45 couples had children. The remaining couples described their relationships as unimproved, and among this group, 5 couples had children. (Hint: Using a frequency analysis, begin with the 100 couples, first branch into the number of couples with improved and unimproved relationships, then under each of these numbers, branch into the number of couples with children and without children. Enter a number at each point of the diagram before proceeding.) (a) What is the probability of randomly selecting a couple who described their relationship as improved? (b) What is the probability of randomly selecting a couple with children? (c) What is the conditional probability of randomly selecting a couple with children, given that their relationship was described as improved? (d) What is the conditional probability of randomly selecting a couple without children, given that their relationship was described as not improved? (e) What is the conditional probability of an improved relationship, given that a couple has children?

As subjects arrive to participate in an experiment, tables of random numbers are used to make random assignments to either group A or group B. (To ensure equal numbers of subjects in the two groups, alternate subjects are automatically assigned to the other, smaller group.) Indicate with a Yes or No whether each of the following rules would work: (a) Assign the subject to group \(\mathrm{A}\) if the random number is even and to group \(\mathrm{B}\) if the random number is odd. (b) Assign the subject to group A if the first digit of the random number is between \(\mathbf{O}\) and 4 and to group \(\mathrm{B}\) if the first digit is between 5 and \(9 .\) (c) Assign the subject to group A if the first two digits of the random number are between 00 and 40 and to group \(\mathrm{B}\) if the first two digits are between 41 and \(99 .\) (d) Assign the subject to group A if the first three digits of the random number are between 000 and 499 and to group \(\mathrm{B}\) if the first three digits are between 500 and \(999 .\)

In Against All Odds, the TV series on statistics (available at http://www.learner.org/ resources/series65.html), statistician Bruce Hoadley discusses the catastrophic failure of the Challenger space shuttle in \(1986 .\) Hoadley estimates that there was a failure probability of .02 for each of the six 0-rings (designed to prevent the escape of potentially explosive burning gases from the joints of the segmented rocket boosters). (a) What was the success probability of each 0-ring? (b) Given that the six 0-rings function independently of each other, what was the probability that all six 0 -rings would succeed, that is, perform as designed? In other words, what was the success probability of the first 0 -ring and the second 0 -ring and the third 0 -ring, and so forth? (c) Given that you know the probability that all six 0-rings would succeed (from the previous question), what was the probability that at least one 0 -ring would fail? (Hint: Use your answer to the previous question to solve this problem.) (d) Given the abysmal failure rate revealed by your answer to the previous question, why, you might wonder, was this space mission even attempted? According to Hoadley, missile engineers thought that a secondary set of 0 -rings would function independently of the primary set of 0 -rings. If true and if the failure probability of each of the secondary 0-rings was the same as that for each primary 0-ring (.02), what would be the probability that both the primary and secondary 0 -rings would fail at any one joint? (Hint: Concentrate on the present question, ignoring your answers to previous questions.)

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