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Fatimah wants to estimate the proportion of students at her school who ate breakfast every day last week. She takes an SRS of 80 of the 1000 students at her school and finds that 20 of those sampled ate breakfast every day last week. Based on this sample, which of the following is a \( 95 \% \) confidence interva for the proportion of all students at the school who ate breakfast every day last week? Choose 1 answer: (A) \( 20 \pm 0.080 \) (B) \( 20 \pm 0.095 \) (C) \( 0.25 \pm 0.080 \) (D) \( 0.25 \pm 0.095 \)

Ask by Erickson Barker. in the United States
Feb 26,2025

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Answer

The 95% confidence interval for the proportion is 0.25 ± 0.095, so the correct answer is (D).

Solution

First, we calculate the sample proportion (p̂) of students who ate breakfast every day:   p̂ = 20/80 = 0.25 Next, the standard error (SE) for a proportion is given by:   SE = √[p̂(1 − p̂) / n]     = √[0.25 × 0.75 / 80]     = √[0.1875 / 80]     = √0.00234375 ≈ 0.0484 For a 95% confidence interval, we use a critical value of approximately 1.96. Thus, the margin of error (ME) is:   ME = 1.96 × 0.0484 ≈ 0.095 So, the 95% confidence interval for the proportion is:   0.25 ± 0.095 Comparing with the given options, the correct answer is:   (D) 0.25 ± 0.095

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To estimate the proportion of students who ate breakfast every day last week, we first calculate the sample proportion. Fatimah found that 20 out of 80 students ate breakfast, giving us a sample proportion \( p̂ = 20/80 = 0.25 \). Now we can calculate the confidence interval for the population proportion. The formula for a confidence interval for proportions is given by \( p̂ \pm z \cdot \sqrt{\frac{p̂(1 - p̂)}{n}} \), where \( z \) is the z-score corresponding to the desired confidence level (1.96 for 95%). This leads us to calculate the standard error and thus the interval. Upon evaluating, we find that the correct answer is: **(D) \( 0.25 \pm 0.095 \)** – The interval suggests that we’re fairly certain the true proportion of breakfast eaters lies between approximately 0.155 and 0.345. Now you’re equipped with a solid understanding of estimating proportions!

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