Math Problem Statement

A baseball player has a lifetime batting average of 0.188. If, in a season, this player has 295 "at bats", what is the probability he gets 34 or more hits? Let H denote the number of hits.

Find the probability that the player gets 34 or more hits.

Solution

To solve this problem, we can model the number of hits HH as a binomial random variable, since each at-bat can be considered a Bernoulli trial where a hit occurs with a certain probability.

Step-by-Step Solution:

  1. Define the parameters:

    • Let pp be the probability of getting a hit (batting average). p=0.188p = 0.188
    • Let nn be the number of at-bats in the season. n=295n = 295

    HBinomial(n,p)H \sim \text{Binomial}(n, p)

  2. Calculate the expected number of hits:

    • The mean μ\mu of a binomial distribution is calculated as: μ=np=2950.18855.46\mu = n \cdot p = 295 \cdot 0.188 \approx 55.46
    • The variance σ2\sigma^2 is: σ2=np(1p)=2950.1880.81245.08\sigma^2 = n \cdot p \cdot (1 - p) = 295 \cdot 0.188 \cdot 0.812 \approx 45.08
    • The standard deviation σ\sigma: σ45.086.71\sigma \approx \sqrt{45.08} \approx 6.71
  3. Use a normal approximation to the binomial distribution: Since nn is large (295), we can use the normal approximation to the binomial distribution: HN(μ,σ2)=N(55.46,45.08)H \approx N(\mu, \sigma^2) = N(55.46, 45.08)

  4. Apply the continuity correction: To approximate the probability P(H34)P(H \geq 34) using the normal distribution, we apply a continuity correction: P(H34)P(Z340.555.466.71)P(H \geq 34) \approx P\left(Z \geq \frac{34 - 0.5 - 55.46}{6.71}\right) P(H34)P(Z21.966.71)P(H \geq 34) \approx P\left(Z \geq \frac{-21.96}{6.71}\right) P(H34)P(Z3.27)P(H \geq 34) \approx P(Z \geq -3.27)

  5. Find the cumulative probability: Using standard normal distribution tables or a calculator: P(Z3.27)0.9994P(Z \geq -3.27) \approx 0.9994

Final Answer:

The probability that the player gets 34 or more hits in the season is approximately 0.9994.

Would you like further details or have any questions?

Related Questions:

  1. How would the probability change if the player’s batting average increased to 0.200?
  2. What is the expected number of hits for this player if they have 500 at-bats?
  3. How does the continuity correction impact the approximation accuracy?
  4. What would be the probability of the player getting fewer than 20 hits?
  5. If the player had 50 at-bats, could we still use the normal approximation?

Tip:

The normal approximation is best used when nn is large and pp is not too close to 0 or 1. For small nn or extreme values of pp, the binomial distribution should be used directly.

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Math Problem Analysis

Mathematical Concepts

Probability
Statistics
Normal Approximation
Binomial Distribution

Formulas

Mean of Binomial Distribution: μ = n * p
Variance of Binomial Distribution: σ² = n * p * (1 - p)
Normal Approximation with Continuity Correction: P(H >= 34) ≈ P(Z >= (x - 0.5 - μ) / σ)

Theorems

Central Limit Theorem (for normal approximation of binomial distribution)

Suitable Grade Level

Undergraduate Level