Math Problem Statement

You may need to use the appropriate appendix table to answer this question. Automobile repair costs continue to rise with the average cost now at $367 per repair.† Assume that the cost for an automobile repair is normally distributed with a standard deviation of $88. Answer the following questions about the cost of automobile repairs. (a) What is the probability that the cost will be more than $460? (Round your answer to four decimal places.) 0.15876

Incorrect: Your answer is incorrect. (b) What is the probability that the cost will be less than $250? (Round your answer to four decimal places.) 0.1587

Incorrect: Your answer is incorrect. (c) What is the probability that the cost will be between $250 and $460? (Round your answer to four decimal places.) 0.6826

Incorrect: Your answer is incorrect. (d) If the cost for your car repair is in the lower 5% of automobile repair charges, what is your maximum possible cost in dollars? (Round your answer to the nearest cent.) $ 224.54

Incorrect: Your answer is incorrect.

Solution

To solve these questions, we'll use the properties of the normal distribution, specifically the Z-score formula and standard normal distribution tables (or a calculator).

Given:

  • Mean (μ) = $367
  • Standard Deviation (σ) = $88

(a) Probability that the cost will be more than $460

  1. Calculate the Z-score: Z=Xμσ=46036788=93881.057Z = \frac{X - \mu}{\sigma} = \frac{460 - 367}{88} = \frac{93}{88} \approx 1.057

  2. Find the probability from the Z-table: Look up Z=1.057Z = 1.057. The cumulative probability for Z=1.057Z = 1.057 is approximately 0.8554.

  3. Calculate the probability of being more than $460: P(X>460)=1P(Z<1.057)=10.85540.1446P(X > 460) = 1 - P(Z < 1.057) = 1 - 0.8554 \approx 0.1446

(b) Probability that the cost will be less than $250

  1. Calculate the Z-score: Z=25036788=117881.33Z = \frac{250 - 367}{88} = \frac{-117}{88} \approx -1.33

  2. Find the probability from the Z-table: Look up Z=1.33Z = -1.33. The cumulative probability for Z=1.33Z = -1.33 is approximately 0.0918.

(c) Probability that the cost will be between $250 and $460

  1. Using previously found probabilities: P(250<X<460)=P(X<460)P(X<250)=P(Z<1.057)P(Z<1.33)P(250 < X < 460) = P(X < 460) - P(X < 250) = P(Z < 1.057) - P(Z < -1.33) From earlier:

    • P(X<460)0.8554P(X < 460) \approx 0.8554
    • P(X<250)0.0918P(X < 250) \approx 0.0918
  2. Calculate: P(250<X<460)=0.85540.09180.7636P(250 < X < 460) = 0.8554 - 0.0918 \approx 0.7636

(d) Maximum cost in the lower 5% of automobile repair charges

  1. Find the Z-score corresponding to the lower 5%: The Z-score for the lower 5% is approximately -1.645.

  2. Calculate the maximum cost: X=μ+Zσ=367+(1.645)(88)367145.56221.44X = \mu + Z\sigma = 367 + (-1.645)(88) \approx 367 - 145.56 \approx 221.44

Summary of Results:

  • (a) P(X>460)0.1446P(X > 460) \approx 0.1446
  • (b) P(X<250)0.0918P(X < 250) \approx 0.0918
  • (c) P(250<X<460)0.7636P(250 < X < 460) \approx 0.7636
  • (d) Maximum cost in the lower 5% is approximately $221.44.

If you would like further details or clarifications, feel free to ask! Here are some related questions you might consider:

  1. How do you interpret the results of normal distribution probabilities?
  2. What other factors could influence automobile repair costs?
  3. How would changes in the mean or standard deviation affect the probabilities?
  4. What is the significance of the lower 5% in practical terms?
  5. Can you explain the concept of Z-scores in more detail?

Tip: Always ensure that you round correctly based on the context of the problem, as it can significantly affect your final answers.

Ask a new question for Free

By Image

Drop file here or Click Here to upload

Math Problem Analysis

Mathematical Concepts

Probability
Normal Distribution
Z-scores

Formulas

Z = (X - μ) / σ
P(X > a) = 1 - P(Z < z)
P(a < X < b) = P(X < b) - P(X < a)

Theorems

Properties of the normal distribution
Central Limit Theorem

Suitable Grade Level

Grades 11-12