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On a test that has a normal distribution...

On a test that has a normal distribution of scores of 59 falls two standard deviations below the mean, and score of 74 is one standard deviation above the mean. If x is an integer score that lies between 2.5 and 3.0 standard deviations above the means. What is a possible value of x?

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To solve the problem, we need to find the integer score \( x \) that lies between 2.5 and 3.0 standard deviations above the mean, given the scores of 59 and 74 in relation to the mean and standard deviation. ### Step-by-Step Solution: 1. **Define the Mean and Standard Deviation**: Let the mean be represented by \( \mu \) and the standard deviation by \( \sigma \). 2. **Set Up the Equations**: - From the information that 59 falls two standard deviations below the mean, we can write: \[ \mu - 2\sigma = 59 \quad \text{(1)} \] - From the information that 74 is one standard deviation above the mean, we can write: \[ \mu + \sigma = 74 \quad \text{(2)} \] 3. **Solve the Equations**: - We can subtract equation (1) from equation (2): \[ (\mu + \sigma) - (\mu - 2\sigma) = 74 - 59 \] Simplifying this gives: \[ 3\sigma = 15 \] Therefore, \[ \sigma = \frac{15}{3} = 5 \] 4. **Find the Mean**: - Now, substitute \( \sigma = 5 \) back into equation (2) to find \( \mu \): \[ \mu + 5 = 74 \] Thus, \[ \mu = 74 - 5 = 69 \] 5. **Determine the Range for \( x \)**: - We need to find the range for \( x \) which lies between 2.5 and 3.0 standard deviations above the mean: \[ \mu + 2.5\sigma < x < \mu + 3.0\sigma \] - Substitute the values of \( \mu \) and \( \sigma \): \[ 69 + 2.5 \times 5 < x < 69 + 3.0 \times 5 \] This simplifies to: \[ 69 + 12.5 < x < 69 + 15 \] Therefore: \[ 81.5 < x < 84 \] 6. **Identify Possible Integer Values**: - The integers that lie between 81.5 and 84 are 82 and 83. ### Conclusion: Thus, the possible integer values of \( x \) are **82 and 83**.
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ENGLISH SAT-PRACTICE TEST 1-EXERCISE
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