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In Exercise 4.92 you found the probability distribution for \(x\), the number of sets required to play a best-of-five-sets match, given that the probability that \(A\) wins any one set \(-\) call this \(P(A)-\) is .6 a. Find the expected number of sets required to complete the match for \(P(A)=.6\). b. Find the expected number of sets required to complete the match when the players are of equal ability- that is, \(P(A)=.5\). c. Find the expected number of sets required to complete the match when the players differ greatly in ability - that is, say, \(P(A)=.9\). d. What is the relationship between \(P(A)\) and \(E(x),\) the expected number of sets required to complete the match?

Short Answer

Expert verified
In a best-of-five-sets match, the expected number of sets required to complete the match can be calculated using the probability distribution for x, which accounts for the possibility of needing 3, 4, or 5 sets based on the probability of player A winning each set and player B's complementary probability. The relationship between P(A) and E(x) is inversely related; as the probability of player A winning each set increases, the expected number of sets required to complete the match decreases, and vice versa. This means that as the two players' abilities become more equal, the match tends to require more sets to be resolved.

Step by step solution

01

Set up the probability distribution for x.

We know that player A must win 3 sets to win the match. There are four possible cases for the number of sets required to complete a game: 3, 4, 5, and "the match cannot be completed." We can calculate the probability for each scenario as follows: - 3 sets: A wins all 3 sets, and the probability is \(P^3_A\). - 4 sets: A wins 3 sets, and B wins 1 set; the probability is \((P_A^3)(1-P_A)\). - 5 sets: A wins 3 sets, and B wins 2 sets; the probability is \((P_A^3)(1-P_A)^2\). - The match cannot be completed: The probability is \(0\) since it's a best-of-five-sets match.
02

Calculate E(x) for P(A) = 0.6.

Using the probability distribution from Step 1, we can calculate the expected number of sets E(x) as follows: - \(E(x) = (3)(P^3_A) + (4)(P^3_A)(1-P_A) + (5)(P^3_A)(1-P_A)^2\) - \(E(x) = (3)(0.6^3) + (4)(0.6^3)(1-0.6) + (5)(0.6^3)(1-0.6)^2\) - \(E(x) \approx 4.296\) So, the expected number of sets required to complete the match for \(P(A)=0.6\) is approximately 4.296.
03

Calculate E(x) for P(A) = 0.5.

Using the same formula, we can calculate E(x) for equal ability players, where \(P(A)=0.5\): - \(E(x) = (3)(0.5^3) + (4)(0.5^3)(1-0.5) + (5)(0.5^3)(1-0.5)^2\) - \(E(x) = 3.75\) So, the expected number of sets required to complete the match for \(P(A)=0.5\) is 3.75.
04

Calculate E(x) for P(A) = 0.9.

Finally, calculating E(x) for players with a significant ability difference, where \(P(A)=0.9\): - \(E(x) = (3)(0.9^3) + (4)(0.9^3)(1-0.9) + (5)(0.9^3)(1-0.9)^2\) - \(E(x) \approx 3.35\) So, the expected number of sets required to complete the match for \(P(A)=0.9\) is approximately 3.35.
05

Investigate the relationship between P(A) and E(x).

From the calculated expected number of sets required in the different scenarios, it's clear that as the probability of player A winning, P(A), increases, the expected number of sets E(x) required to complete the match decreases. As players' abilities become more equal, the match tends to require more sets to be completed, with E(x) being the highest when both players have an equal probability of winning each set (0.5). In conclusion, the relationship between P(A) and E(x) is inversely related to each other; as P(A) increases or decreases, E(x) decreases or increases, respectively.

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Key Concepts

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

Expected Value
The expected value, often denoted as \( E(x) \), is a fundamental concept in probability theory. It represents the average or mean value we would expect over many repetitions of a probability experiment. In simpler terms, if you were to play a game numerous times, the expected value gives you an idea of the average outcome you're likely to see.

In the best-of-five-sets match, the expected value of the number of sets needed can be calculated using the probabilities of different scenarios: winning in 3, 4, or 5 sets. We determine the probability for each case, then multiply by the number of sets in that scenario. Finally, we sum these values to get the expected number of sets.

Here's the formula for expected value in this context:
  • \( E(x) = (3)(P^3_A) + (4)(P^3_A)(1-P_A) + (5)(P^3_A)(1-P_A)^2 \)
This approach integrates various possibilities weighted by their probabilities, leading to a meaningful average outcome.
Probability Theory
Probability theory is the branch of mathematics dealing with random events and outcomes. It helps us quantify uncertainty and predict the likelihood of various outcomes in a given scenario. In the context of our tennis match, probability theory allows us to determine the likelihood of player A winning different numbers of sets.

Consider a player A who has a probability \( P(A) \) of winning any given set. If \( P(A) = 0.6 \), for instance, player A has a 60% chance of winning each set. By employing probability theory, we can compute the chances of A winning the match in 3, 4, or 5 sets:
  • Winning in exactly 3 sets: \( P^3_A \)
  • Winning in exactly 4 sets: \( P^3_A (1 - P_A) \)
  • Winning in exactly 5 sets: \( P^3_A (1 - P_A)^2 \)
By considering these probabilities, we can paint a comprehensive picture of how likely different match outcomes are.
Statistical Analysis
Statistical analysis involves collecting, examining, interpreting, and presenting data. Through this analysis, we can gain insights and make more informed decisions. When analyzing a probability distribution, especially in sports, there are key trends and relationships that become clear through statistical examination.

For instance, in our exercise, statistical analysis reveals a clear relationship between the probability \( P(A) \) of player A winning any set and the expected number of sets \( E(x) \) needed to complete the match. As \( P(A) \) increases, the expected number of sets \( E(x) \) tends to decrease. This inverse relationship suggests that when a player is more dominant (higher \( P(A) \)), fewer sets are required, as there is a higher likelihood of winning without needing multiple sets. Conversely, equally matched players spend more time competing, requiring potentially more sets.

Thus, statistical analysis helps us uncover such patterns and make predictions about game outcomes based on probabilities.

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