Developing Theoretical Probability Distributions, Expected Value
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Statistics › Developing Theoretical Probability Distributions, Expected Value
A game uses a bag containing 5 equally likely tickets labeled $A,B,C,D,E$. One ticket is drawn at random. Define the random variable $X$ by the mapping: $X=-2$ if $A$ is drawn; $X=0$ if $B$ or $C$ is drawn; and $X=3$ if $D$ or $E$ is drawn. What is the expected value of $X$ based on this theoretical model?
$\dfrac{4}{5}$
$\dfrac{3}{5}$
$\dfrac{1}{5}$
$\dfrac{3+0+(-2)}{3}=\dfrac{1}{3}$
Explanation
This problem involves developing a theoretical probability distribution from a bag of tickets. The model has 5 equally likely tickets {A,B,C,D,E}, each with probability 1/5. The random variable X maps: X=-2 when A is drawn, X=0 when B or C is drawn, and X=3 when D or E is drawn. To find P(X=x), we count tickets: P(X=-2) = P(A) = 1/5, P(X=0) = P(B)+P(C) = 2/5, and P(X=3) = P(D)+P(E) = 2/5. The expected value is E(X) = (-2)(1/5) + 0(2/5) + 3(2/5) = -2/5 + 0 + 6/5 = 4/5. A common misconception is thinking X-values {-2,0,3} are equally likely with probability 1/3 each, or averaging the X-values directly as (3+0+(-2))/3. The strategy: identify which tickets give each X-value → count them → calculate probabilities as fractions of 5.
A fair die is rolled and a fair coin is flipped. The 12 outcomes in the sample space are equally likely. Define the random variable $X$ as follows: $X=1$ if the coin shows heads and the die shows a number greater than 4; otherwise $X=0$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=0)=\tfrac{11}{12},\ P(X=1)=\tfrac{1}{12}$
$P(X=0)=\tfrac{5}{6},\ P(X=1)=\tfrac{1}{6}$
$P(X=0)=\tfrac{5}{12},\ P(X=1)=\tfrac{7}{12}$
$P(X=0)=\tfrac{5}{12},\ P(X=1)=\tfrac{1}{12}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the 12 equally likely outcomes of a fair die roll and coin flip, each with probability 1/12. Each outcome maps to X=1 if the coin is heads and die >4 (i.e., heads with 5 or 6), otherwise X=0. The probability P(X=x) is determined by counting favorable outcomes: P(X=1)=2/12=1/6, P(X=0)=10/12=5/6. The expected value E(X) is computed as 1*(1/6) + 0*(5/6) = 1/6. A common misconception is that all X-values are equally likely, but X=0 is far more probable due to the conditions. To solve similar problems, list all outcomes, map each to its X, and combine probabilities for each distinct x.
A bag contains 4 equally likely cards labeled $1,2,3,4$. One card is drawn at random. Define the random variable $X$ by the explicit mapping: $1\mapsto -1$, $2\mapsto 0$, $3\mapsto 0$, $4\mapsto 2$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=-1)=\tfrac{1}{3},\ P(X=0)=\tfrac{1}{3},\ P(X=2)=\tfrac{1}{3}$
$P(X=-1)=\tfrac{1}{4},\ P(X=0)=\tfrac{1}{4},\ P(X=2)=\tfrac{1}{4}$
$P(X=-1)=\tfrac{1}{4},\ P(X=0)=\tfrac{1}{2},\ P(X=2)=\tfrac{1}{4}$
$P(1)=\tfrac{1}{4},\ P(2)=\tfrac{1}{4},\ P(3)=\tfrac{1}{4},\ P(4)=\tfrac{1}{4}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the equally likely cards labeled 1 through 4, each with probability 1/4. Each card maps to an X-value via the explicit rule: 1 to -1, 2 to 0, 3 to 0, and 4 to 2. The probability P(X=x) is determined by summing probabilities of cards mapping to each x, resulting in P(X=-1)=1/4, P(X=0)=2/4=1/2, and P(X=2)=1/4. The expected value E(X) is computed as (-1)(1/4) + 0(1/2) + 2*(1/4) = (-1/4 + 0 + 2/4) = 1/4. A common misconception is that all X-values are equally likely, but P(X=0) is higher due to multiple mappings. To solve similar problems, list all outcomes, map each to its X, and combine probabilities for each distinct x.
A fair six-sided die is rolled once (each of $1$–$6$ equally likely). Define the random variable $X$ by the mapping: odd outcomes ${1,3,5}\mapsto 1$ and even outcomes ${2,4,6}\mapsto 4$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=1)=\tfrac{1}{2},\ P(X=4)=\tfrac{1}{2}$
$P(X=1)=\tfrac{1}{6},\ P(X=4)=\tfrac{5}{6}$
$P(X=1)=\tfrac{1}{4},\ P(X=4)=\tfrac{3}{4}$
$P(X=1)=\tfrac{1}{3},\ P(X=4)=\tfrac{2}{3}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the six equally likely outcomes of a fair die roll, each with probability 1/6. Outcomes map to X-values: odd numbers (1,3,5) to 1 and even numbers (2,4,6) to 4. The probability P(X=x) is determined by counting outcomes per x, giving P(X=1)=3/6=1/2 and P(X=4)=3/6=1/2. The expected value E(X) is computed as 1*(1/2) + 4*(1/2) = (1/2 + 4/2) = 5/2. A common misconception is that all X-values are equally likely only if outcome counts match, but here they are equal due to balanced mappings. To solve similar problems, list all outcomes, map each to its X, and combine probabilities for each distinct x.
A fair coin is flipped 3 times. The sample space consists of all equally likely length-3 sequences of H and T. Define the random variable $X$ as the number of heads in the 3 flips. Which table correctly represents the theoretical probability distribution of $X$ (using $P(X=x)$ derived from the fraction of outcomes that produce each $x$)?
$P(X=0)=\tfrac{1}{4},\ P(X=1)=\tfrac{1}{4},\ P(X=2)=\tfrac{1}{4},\ P(X=3)=\tfrac{1}{4}$
$P(X=0)=\tfrac{1}{8},\ P(X=1)=\tfrac{3}{8},\ P(X=2)=\tfrac{3}{8},\ P(X=3)=\tfrac{1}{8}$
$P(X=0)=\tfrac{1}{8},\ P(X=1)=\tfrac{2}{8},\ P(X=2)=\tfrac{4}{8},\ P(X=3)=\tfrac{1}{8}$
$P(\text{HHH})=\tfrac{1}{8},\ P(\text{HHT})=\tfrac{1}{8},\ P(\text{HTH})=\tfrac{1}{8},\ P(\text{THH})=\tfrac{1}{8}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the equally likely outcomes in the sample space of three fair coin flips, consisting of 8 sequences each with probability 1/8. Each outcome sequence maps to an X-value defined as the number of heads in the sequence. The probability P(X=x) is determined by counting the sequences with exactly x heads and dividing by 8, resulting in P(X=0)=1/8, P(X=1)=3/8, P(X=2)=3/8, and P(X=3)=1/8. The expected value E(X) is computed as the sum of x times P(X=x), yielding 0*(1/8) + 1*(3/8) + 2*(3/8) + 3*(1/8) = 12/8 = 3/2. A common misconception is that all X-values are equally likely, but X=1 and X=2 have higher probabilities due to more supporting outcomes. To solve similar problems, list all outcomes, map each to its X value, and combine probabilities for each distinct x.
Two fair coins are flipped once each, producing 4 equally likely outcomes: ${\text{HH, HT, TH, TT}}$. Define the random variable $X$ by the explicit mapping: $\text{HH}\mapsto 2$, $\text{HT}\mapsto 0$, $\text{TH}\mapsto 0$, $\text{TT}\mapsto -1$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=-1)=\tfrac{1}{4},\ P(X=2)=\tfrac{1}{4}$
$P(X=-1)=\tfrac{1}{3},\ P(X=0)=\tfrac{1}{3},\ P(X=2)=\tfrac{1}{3}$
$P(X=-1)=\tfrac{1}{2},\ P(X=0)=\tfrac{1}{4},\ P(X=2)=\tfrac{1}{4}$
$P(X=-1)=\tfrac{1}{4},\ P(X=0)=\tfrac{1}{2},\ P(X=2)=\tfrac{1}{4}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the four equally likely outcomes of two fair coin flips, each with probability 1/4. Each outcome maps explicitly to an X-value: HH to 2, HT to 0, TH to 0, and TT to -1. The probability P(X=x) is determined by grouping outcomes: P(X=2)=1/4, P(X=0)=2/4=1/2, P(X=-1)=1/4. The expected value E(X) is computed as 2*(1/4) + 0*(1/2) + (-1)*(1/4) = (2/4 + 0 - 1/4) = 1/4. A common misconception is that all X-values are equally likely, but P(X=0) is twice as likely due to more mappings. To solve similar problems, list all outcomes, map each to its X, and combine probabilities for each distinct x.
A spinner is divided into 5 equal sectors labeled $A,B,C,D,E$, so each outcome is equally likely. Define the random variable $X$ by the mapping: $A\mapsto 0$, $B\mapsto 0$, $C\mapsto 1$, $D\mapsto 2$, $E\mapsto 5$. What is the expected value of $X$?
$\tfrac{8}{5}$
$\tfrac{5}{2}$
$\tfrac{6}{5}$
$\tfrac{8}{3}$
Explanation
This problem involves developing theoretical probability distributions and calculating expected values for discrete random variables. In this model, probabilities are derived from the five equally likely sectors of the spinner, each with probability 1/5. Each sector maps to an X-value: A and B to 0, C to 1, D to 2, and E to 5. The probability P(X=x) is determined by summing probabilities per x, yielding P(X=0)=2/5, P(X=1)=1/5, P(X=2)=1/5, P(X=5)=1/5. The expected value E(X) is computed as 0*(2/5) + 1*(1/5) + 2*(1/5) + 5*(1/5) = (0 + 1/5 + 2/5 + 5/5) = 8/5. A common misconception is assuming equal likelihood for all X-values, but P(X=0) is higher due to multiple sectors. To solve similar problems, list all outcomes, map each to its X, and combine probabilities before calculating E(X).
Two fair coins are flipped; all 4 outcomes are equally likely: ${\text{HH},\text{HT},\text{TH},\text{TT}}$. Define the random variable $X$ as follows: $X=2$ if both flips match (HH or TT) and $X=0$ otherwise (HT or TH). The mapping is ${\text{HH},\text{TT}}\to 2$ and ${\text{HT},\text{TH}}\to 0$. What is the expected value of $X$ based on this theoretical model?
$1$
$\frac{1}{2}$
$2$
$0$
Explanation
This scenario involves theoretical probability distributions and expected value for matching coin flips. Probabilities arise from the uniform model over four equally likely outcomes. Outcomes map to X=2 for matches {HH, TT} and X=0 for mismatches {HT, TH}. Thus, P(X=2) = 2/4 = 1/2 and P(X=0) = 2/4 = 1/2. The expected value is E[X] = 2*(1/2) + 0*(1/2) = 1. A common misconception is assuming all X-values equally likely without considering outcome counts, but here they are balanced. For similar problems, list all outcomes, map to X-categories, and combine probabilities accordingly.
A fair six-sided die is rolled once; outcomes are equally likely. Define the random variable $X$ as $X=\lvert\text{roll}-3\rvert$. The outcome-to-$X$ mapping is: $1\to 2$, $2\to 1$, $3\to 0$, $4\to 1$, $5\to 2$, $6\to 3$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=0)=\frac{1}{6},;P(X=1)=\frac{2}{6},;P(X=2)=\frac{2}{6}$
$P(X=0)=\frac{1}{4},;P(X=1)=\frac{1}{4},;P(X=2)=\frac{1}{4},;P(X=3)=\frac{1}{4}$
$P(X=0)=\frac{1}{6},;P(X=1)=\frac{2}{6},;P(X=2)=\frac{2}{6},;P(X=3)=\frac{1}{6}$
$P(X=0)=\frac{1}{6},;P(X=1)=\frac{1}{6},;P(X=2)=\frac{2}{6},;P(X=3)=\frac{2}{6}$
Explanation
This problem covers theoretical probability distributions and expected value for absolute deviation on a die. Probabilities come from the uniform model with six equally likely outcomes. Outcomes map to X = |roll - 3|, yielding 3 to 0, 2 and 4 to 1, 1 and 5 to 2, and 6 to 3. Hence, P(X=0) = 1/6, P(X=1) = 2/6, P(X=2) = 2/6, P(X=3) = 1/6, as in choice A. This supports E[X] = 0*(1/6) + 1*(2/6) + 2*(2/6) + 3*(1/6) = 4/3. A misconception is equal probability for each X, but it varies with mapped outcomes. For like problems, list outcomes, compute X for each, and aggregate probabilities per X-value.
A fair coin is flipped 3 times; all $2^3=8$ outcomes are equally likely. Define the random variable $X$ as the number of heads. The outcomes map to $X$ as follows: $\text{TTT}\to 0$; $\text{HTT, THT, TTH}\to 1$; $\text{HHT, HTH, THH}\to 2$; $\text{HHH}\to 3$. Which table correctly represents the theoretical probability distribution of $X$?
$P(X=0)=\frac{1}{8},;P(X=1)=\frac{3}{8},;P(X=2)=\frac{3}{8},;P(X=3)=\frac{1}{8}$
$P(\text{TTT})=\frac{1}{8},;P(\text{HTT})=\frac{1}{8},;P(\text{THT})=\frac{1}{8},;P(\text{TTH})=\frac{1}{8}$
$P(X=0)=\frac{1}{4},;P(X=1)=\frac{1}{4},;P(X=2)=\frac{1}{4},;P(X=3)=\frac{1}{4}$
$P(X=0)=\frac{1}{8},;P(X=1)=\frac{1}{8},;P(X=2)=\frac{3}{8},;P(X=3)=\frac{3}{8}$
Explanation
This problem addresses theoretical probability distributions and expected value for the number of heads in coin flips. Probabilities are derived from the uniform model over 8 equally likely outcomes of three fair coin flips. Outcomes map to X-values based on head count: one outcome to X=0, three to X=1, three to X=2, and one to X=3. Thus, P(X=0) = 1/8, P(X=1) = 3/8, P(X=2) = 3/8, and P(X=3) = 1/8, matching choice A. This distribution justifies an expected value of E[X] = 0*(1/8) + 1*(3/8) + 2*(3/8) + 3*(1/8) = 1.5, though not asked. A misconception is assuming equal likelihood for each X-value, but probabilities vary with the number of supporting outcomes. For similar problems, list all outcomes, map to X, and combine probabilities by counting outcomes per X-value.