Math Problem Statement

Suppose Z follows the standard normal distribution. Find the value of c such that P(-c ≤ Z ≤ c) = 0.9729.

Solution

The problem asks us to find the value of cc such that:

P(cZc)=0.9729P(-c \leq Z \leq c) = 0.9729

where ZZ follows a standard normal distribution (mean 0, standard deviation 1). This is essentially asking for the symmetric range around 0 where the total probability is 0.9729.

Step-by-Step Solution:

  1. Understanding the Probability: The probability P(cZc)=0.9729P(-c \leq Z \leq c) = 0.9729 implies that the probability outside this range is 10.9729=0.02711 - 0.9729 = 0.0271. Since the normal distribution is symmetric, half of this remaining probability (i.e., 0.01355) is in each tail.

    Therefore, the probability that ZZ is greater than cc or less than c-c is 0.01355 in each tail.

  2. Using the Z-Table or Inverse Standard Normal: We need to find the Z-score that corresponds to a cumulative probability of 10.01355=0.986451 - 0.01355 = 0.98645 (this is the cumulative probability to the left of cc).

    Using a standard normal Z-table or a calculator:

    • For P(Zc)=0.98645P(Z \leq c) = 0.98645, we look up the corresponding Z-score.
    • From the table, Z=2.17Z = 2.17 corresponds to a cumulative probability of 0.9864.
  3. Conclusion: Thus, c=2.17c = 2.17.

Therefore, the value of cc is approximately 2.17.

Would you like further details on any part of this solution or have questions? Here are five related questions you might find helpful:

  1. What is the Z-score and how is it used in normal distribution?
  2. How do we interpret the probability in standard normal distribution problems?
  3. What are the key characteristics of the standard normal distribution?
  4. How do cumulative probability tables work in finding Z-scores?
  5. How can I calculate the Z-score without using a table?

Tip: In standard normal problems, knowing how to use Z-tables or the inverse normal function on calculators is essential for finding specific probabilities.

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Math Problem Analysis

Mathematical Concepts

Probability
Standard Normal Distribution
Z-scores

Formulas

P(-c ≤ Z ≤ c) = cumulative probability
Z = (X - μ) / σ

Theorems

Standard Normal Distribution
Symmetry of Normal Distribution

Suitable Grade Level

College/University