Pregunta
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he mean value of land and buildings per acre from a sample of farms is \( \$ 1500 \), with a standard deviation of \( \$ 100 \) The data set has a bell-shaped distribution. Assume the number of farms in the sample is 80 (a) Use the empirical rule to estimate the number of farms whose land and building values per acre are between \( \$ 1300 \) and \( \$ 1700 \). 76 farms (Round to the nearest whole number as needed.) (b) If 21 additional farms were sampled, about how many of these additional farms would you expect to have land and building values between \( \$ 1300 \) per acre and \( \$ 1700 \) per acre? farms out of 21 (Round to the nearest whole number as needed.)

Ask by Best Sanders. in the United States
Feb 13,2025

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(a) About 76 farms have land and building values between $1300 and $1700 per acre. (b) Out of 21 additional farms, you would expect approximately 20 to have values between $1300 and $1700 per acre.

Solución

We are given a sample of 80 farms with a mean land and building value per acre of $1500 and a standard deviation of $100. Since the distribution is bell-shaped (normal), we can apply the empirical rule. Step 1. Determine the z-scores for $1300 and $1700:   - For $1300: (1300 − 1500) / 100 = −2   - For $1700: (1700 − 1500) / 100 = 2 Step 2. The empirical rule tells us that about 95% of the data in a normal distribution lies within ±2 standard deviations of the mean. (a) Number of farms in sample of 80 expected to fall between $1300 and $1700:   95% of 80 = 0.95 × 80 = 76 farms (b) If 21 additional farms were sampled, the same proportion would be expected:   95% of 21 = 0.95 × 21 ≈ 20 farms (rounded to the nearest whole number) So, the answers are:   (a) Approximately 76 farms.   (b) Approximately 20 farms.

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Bonus Knowledge

According to the empirical rule, also known as the 68-95-99.7 rule, in a bell-shaped distribution, approximately 68% of the data falls within one standard deviation of the mean. Here, the mean is \( \$ 1500 \) and the standard deviation is \( \$ 100 \). Therefore, the range from \( \$ 1300 \) to \( \$ 1700 \) is one standard deviation below and above the mean. Since there are 80 farms in the sample, \( 0.68 \times 80 = 54.4 \), which we round to 54 farms. So, approximately 54 farms have land and building values per acre between \( \$ 1300 \) and \( \$ 1700 \). Now, when sampling an additional 21 farms, we still apply the empirical rule. Since we expect the same percentage (68%) to fall within that range, we calculate \( 0.68 \times 21 \approx 14.28 \), rounding to 14. Thus, we would expect about 14 additional farms to have values between \( \$ 1300 \) and \( \$ 1700 \) per acre.

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