Math Problem Statement

A study showed that the average number of hours children in the US watch television each day is 4 hours with a standard deviation of 1.6 hours. If a group of 64 students is selected at random, what is the probability that the average time these children watch television is more than 4.3 hours a day?

Solution

The problem you're dealing with asks to find the probability that the average time children watch TV is more than 4.3 hours, based on a sample of 64 students.

Here’s how to solve this problem step by step:

Step 1: Identify the given information

  • Population mean (μ\mu) = 4 hours
  • Population standard deviation (σ\sigma) = 1.6 hours
  • Sample size (nn) = 64
  • Sample mean = 4.3 hours

Step 2: Apply the Central Limit Theorem

Since the sample size is large (64), we can apply the Central Limit Theorem. The sampling distribution of the sample mean will be approximately normally distributed with:

  • Mean of the sample distribution = Population mean = 4 hours
  • Standard deviation of the sample mean (standard error): σxˉ=σn=1.664=1.68=0.2\sigma_{\bar{x}} = \frac{\sigma}{\sqrt{n}} = \frac{1.6}{\sqrt{64}} = \frac{1.6}{8} = 0.2

Step 3: Calculate the z-score

The z-score formula is: z=xˉμσxˉz = \frac{\bar{x} - \mu}{\sigma_{\bar{x}}} Substitute the values: z=4.340.2=0.30.2=1.5z = \frac{4.3 - 4}{0.2} = \frac{0.3}{0.2} = 1.5

Step 4: Find the probability

Now, find the probability that corresponds to a z-score of 1.5. You can use a standard normal distribution table, or a calculator, which gives: P(Z>1.5)=1P(Z1.5)=10.9332=0.0668P(Z > 1.5) = 1 - P(Z \leq 1.5) = 1 - 0.9332 = 0.0668

Conclusion:

The probability that the average time these children watch TV is more than 4.3 hours is 0.0668. Therefore, the correct answer is the second option: 0.0668.

Would you like more details on any part of the solution?


Here are some questions that can help expand your understanding:

  1. How does the sample size affect the standard error of the mean?
  2. What would the z-score be if the average time was 4.5 hours instead of 4.3?
  3. How would the probability change if the standard deviation was 2 hours instead of 1.6 hours?
  4. What happens if the sample size is much smaller, say 10, instead of 64? Can we still apply the Central Limit Theorem?
  5. How would you find the probability for a two-tailed test, i.e., if you were interested in averages both less than 3.7 hours and more than 4.3 hours?

Tip: When dealing with probabilities and normal distributions, using a z-table or software tools like a scientific calculator or Excel can make your calculations faster and more accurate.

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Math Problem Analysis

Mathematical Concepts

Statistics
Normal Distribution
Probability
Z-scores
Central Limit Theorem

Formulas

Z = (X̄ - μ) / (σ / √n)
P(Z > z-score) = 1 - P(Z ≤ z-score)

Theorems

Central Limit Theorem

Suitable Grade Level

Grades 11-12, College-level Introductory Statistics