Math Problem Statement
41% of people say yes and 49% say no out of the whole population. You randomly sample 100 people, what's the probability that a majority of them say yes?
Solution
To solve this, we need to compute the probability that a majority of the sampled 100 people say "yes". This means we want the number of people who say "yes" to be greater than 50 out of the 100.
Step-by-Step Approach:
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Define the Problem:
- Probability of a single person saying "yes" is .
- Probability of a single person saying "no" is .
- We sample 100 people, so the total number of people in the sample is .
- We want the probability that more than 50 people say "yes", i.e., we need , where is the number of people saying "yes".
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Use the Binomial Distribution: Since each person's response is independent, the number of "yes" responses follows a binomial distribution: The binomial distribution has the following probability mass function (PMF): However, calculating this probability directly for all values of can be cumbersome. So, we use an approximation.
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Normal Approximation to the Binomial Distribution: The binomial distribution can be approximated by a normal distribution when is large, and this approximation works well here because is sufficiently large.
The parameters for the normal distribution are:
- Mean ():
- Variance ():
- Standard deviation ():
So, can be approximated by:
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Apply the Normal Approximation: To find the probability that more than 50 people say "yes", we need to compute: First, we standardize this to a Z-score using: For , we compute the Z-score:
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Find the Probability: Using the standard normal distribution, we find the probability corresponding to a Z-score of 1.83. The cumulative probability for is approximately 0.9664.
So, the probability of is:
Final Answer:
The probability that a majority of the 100 people say "yes" is approximately 0.0336, or 3.36%.
Would you like more details on any of the steps?
Here are a few follow-up questions:
- How does the normal approximation compare to the exact binomial distribution for this problem?
- What would happen if the probability of "yes" was closer to 0.5?
- How can we use the continuity correction in the normal approximation?
- What are other scenarios where the binomial distribution is approximated by a normal distribution?
- How does increasing the sample size affect the probability of a majority?
Tip: In problems with large , always consider using the normal approximation to simplify calculations, especially when the binomial distribution becomes tedious to compute directly.
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Math Problem Analysis
Mathematical Concepts
Probability
Binomial Distribution
Normal Approximation
Formulas
Binomial distribution: P(X = k) = C(n, k) * p^k * (1 - p)^(n - k)
Normal approximation to binomial: X ~ N(μ = np, σ^2 = np(1 - p))
Z-score: Z = (X - μ) / σ
Theorems
Normal Approximation to the Binomial Distribution
Central Limit Theorem
Suitable Grade Level
Grades 11-12 (Advanced Probability)
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