The mean performance score on a physical fitness test for Division I student-athletes is 947 with a standard deviation of 205. If you select a random sample of 60 of these students, what is the probability the mean is below 900? (Round z-value to 2 decimal places and final answer to 4 decimal places.)
Question
The mean performance score on a physical fitness test for Division I student-athletes is 947 with a standard deviation of 205. If you select a random sample of 60 of these students, what is the probability the mean is below 900? (Round z-value to 2 decimal places and final answer to 4 decimal places.)
Solution
To solve this problem, we will use the concept of Z-score in statistics. The Z-score is a measure of how many standard deviations an element is from the mean.
Step 1: Identify the given values. The population mean (μ) = 947 The standard deviation (σ) = 205 The sample size (n) = 60 The sample mean (x̄) = 900
Step 2: Calculate the standard error of the mean (σx̄). The standard error of the mean is the standard deviation of the sampling distribution of the mean. It is calculated as:
σx̄ = σ/√n = 205/√60 ≈ 26.46
Step 3: Calculate the Z-score. The Z-score is calculated as:
Z = (x̄ - μ) / σx̄ = (900 - 947) / 26.46 ≈ -1.78 (rounded to 2 decimal places)
Step 4: Look up the Z-score in the Z-table to find the probability. The Z-table tells us what percentage of the population is below (to the left of) our score.
Looking up a Z-score of -1.78 in the Z-table gives us a probability of 0.0375.
So, the probability that the mean score of a random sample of 60 students is below 900 is 0.0375 or 3.75% (rounded to 4 decimal places).
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