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Game of dreidel. A dreidel is a four-sided spinning top with the Hebrew letters nun, gimel, hei, and shin, one on each side. Each side is equally likely to come up in a single spin of the dreidel. Suppose you spin a dreidel three times. Calculate the probability of getting (a) at least one nun? (b) exactly 2 nuns? (c) exactly 1 hei? (d) at most 2 gimels?

Short Answer

Expert verified
(a) \( \frac{37}{64} \); (b) \( \frac{9}{64} \); (c) \( \frac{27}{64} \); (d) \( \frac{63}{64} \).

Step by step solution

01

Understand the Probability Basics

The dreidel has four sides with equal probability for each outcome: nun, gimel, hei, and shin. Each has a probability of \( \frac{1}{4} \). When spinning the dreidel three times, the total possible outcomes are \( 4^3 = 64 \).
02

Calculate Probability of Getting at Least One Nun

To find the probability of getting at least one nun, calculate the probability of getting no nuns and then subtract from 1. Probability of not getting a nun in one spin is \( \frac{3}{4} \), and in three spins is \( \left(\frac{3}{4}\right)^3 = \frac{27}{64} \). Thus, the probability of getting at least one nun is \( 1 - \frac{27}{64} = \frac{37}{64} \).
03

Calculate Probability of Exactly 2 Nuns

If exactly 2 nuns occur, then we need the probability for two spins being nuns and one being something else. The number of such favorable outcomes is given by combinations \( \binom{3}{2} = 3 \). The probability calculation is \( 3 \times \left(\frac{1}{4}\right)^2 \times \left(\frac{3}{4}\right)^1 = 3 \times \frac{1}{16} \times \frac{3}{4} = \frac{9}{64} \).
04

Calculate Probability of Exactly 1 Hei

To get exactly 1 hei, the number of favorable outcomes is \( \binom{3}{1} = 3 \). The probability is calculated by \( 3 \times \left(\frac{1}{4}\right)^1 \times \left(\frac{3}{4}\right)^2 = 3 \times \frac{1}{4} \times \frac{9}{16} = \frac{27}{64} \).
05

Calculate Probability of At Most 2 Gimels

Calculate the probability of 0, 1, or 2 gimels. Probability of 0 gimels is \( \left(\frac{3}{4}\right)^3 = \frac{27}{64} \), for exactly 1 gimel is \( 3 \times \frac{1}{4} \times \frac{9}{16} = \frac{27}{64} \), and for exactly 2 gimels is \( 3 \times \frac{1}{16} \times \frac{3}{4} = \frac{9}{64} \). Add them to get at most 2 gimels: \( \frac{27}{64} + \frac{27}{64} + \frac{9}{64} = \frac{63}{64} \).

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Key Concepts

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

Combinatorics
Combinatorics is a branch of mathematics dealing with counting, arranging, and finding patterns in sets of elements. When spinning a dreidel three times, we use combinatorial methods to figure out how many ways specific outcomes occur. For example, to find the probability of getting exactly two nuns, we consider the number of ways to choose which two of the three spins will result in a nun. This is calculated using the combination formula \( \binom{n}{r} \), where \( n \) is the total number of spins, and \( r \) is the number of desired successful outcomes. In this case, it's \( \binom{3}{2} = 3 \). This process highlights the use of combinatorics in determining favorable outcomes, which is fundamental for calculating probabilities when order does not matter.
Discrete Mathematics
Discrete mathematics is the study of mathematical structures that are countable or otherwise distinct and separable. It underlies the dreidel probability problems since we deal with discrete events: the dreidel landing on nun, gimel, hei, or shin. Each outcome in our spinning game is separate and finite; therefore, it forms part of discrete mathematics. Calculating the total number of possible outcomes, \( 4^3 = 64 \), represents a finite set, thus fitting perfectly within discrete mathematics. Discrete mathematics helps us structure problems accurately so we can focus on countable, non-continuous data sets to make our calculations.
Random Variables
A random variable is a quantity resulting from a random event, like spinning a dreidel, which can take different values based on outcomes. In our scenario, each spin of the dreidel is an independent random variable with four possible outcomes: nun, gimel, hei, and shin. When we consider a random variable like \( X \), representing the count of times a nun appears in three spins, it helps us determine different probabilities, such as the chances of getting exactly two nuns. Random variables provide a bridge between the random physical processes and their quantifiable probabilities, allowing us to analyze and predict outcomes in statistical models.
Probability Distributions
Probability distributions describe how the probability is spread over different events or outcomes of a random variable. In the dreidel spin, the probability distribution considers each potential outcome across multiple spins. For example, a nun showing up 0 to 3 times forms its own probability distribution based on our statistical calculations. These distributions can be visualized to understand the likelihood of each specific outcome, providing insights into the behavior of our random variable over multiple trials. In essence, probability distributions enable us to fully picture how likely certain combinations of results are, aiding in deeper predictive analyses.

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Most popular questions from this chapter

Eye color, Part II. Exercise 4.13 introduces a husband and wife with brown eyes who have 0.75 probability of having children with brown eyes, 0.125 probability of having children with blue eyes, and 0.125 probability of having children with green eyes. (a) What is the probability that their first child will have green eyes and the second will not? (b) What is the probability that exactly one of their two children will have green eyes? (c) If they have six children, what is the probability that exactly two will have green eyes? (d) If they have six children, what is the probability that at least one will have green eyes? (e) What is the probability that the first green eyed child will be the \(4^{\text {th }}\) child? (f) Would it be considered unusual if only 2 out of their 6 children had brown eyes?

Rolling a die. Calculate the following probabilities and indicate which probability distribution model is appropriate in each case. You roll a fair die 5 times. What is the probability of rolling (a) the first 6 on the fifth roll? (b) exactly three 6 s? (c) the third 6 on the fifth roll?

Chicken pox, Part I. The National Vaccine Information Center estimates that \(90 \%\) of Americans have had chickenpox by the time they reach adulthood. \({ }^{32}\) (a) Suppose we take a random sample of 100 American adults. Is the use of the binomial distribution appropriate for calculating the probability that exactly 97 out of 100 randomly sampled American adults had chickenpox during childhood? Explain. (b) Calculate the probability that exactly 97 out of 100 randomly sampled American adults had chickenpox during childhood. (c) What is the probability that exactly 3 out of a new sample of 100 American adults have not had chickenpox in their childhood? (d) What is the probability that at least 1 out of 10 randomly sampled American adults have had chickenpox? (e) What is the probability that at most 3 out of 10 randomly sampled American adults have not had chickenpox?

Speeding on the \(1-5,\) Part I. The distribution of passenger vehicle speeds traveling on the Interstate 5 Freeway (I-5) in California is nearly normal with a mean of 72.6 miles/hour and a standard deviation of 4.78 miles/hour. (a) What percent of passenger vehicles travel slower than 80 miles/hour? (b) What percent of passenger vehicles travel between 60 and 80 miles/hour? (c) How fast do the fastest \(5 \%\) of passenger vehicles travel? (d) The speed limit on this stretch of the I-5 is 70 miles/hour. Approximate what percentage of the passenger vehicles travel above the speed limit on this stretch of the \(\mathrm{I}-5\).

The American Community Survey estimates that \(47.1 \%\) of women ages 15 years and over are married. \({ }^{41}\) (a) We randomly select three women between these ages. What is the probability that the third woman selected is the only one who is married? (b) What is the probability that all three randomly selected women are married? (c) On average, how many women would you expect to sample before selecting a married woman? What is the standard deviation? (d) If the proportion of married women was actually \(30 \%\), how many women would you expect to sample before selecting a married woman? What is the standard deviation? (e) Based on your answers to parts (c) and (d), how does decreasing the probability of an event affect the mean and standard deviation of the wait time until success?

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