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2 A certain standardized test's math scores have a bell-shaped distribution with a mean of 525 and a standard deviation of 114. Complete parts (a) through (c). (a) What percentage of standardized test scores is between 183 and 867 ? \( 99.7 \% \) (Round to one decimal place as needed.) (b) What percentage of standardized test scores is less than 183 or greater than 867 ? 12.6 of 17 points \( 0.3 \% \) (Round to one decimal place as needed.) (c) What percentage of standardized test scores is greater than 753 ? \( \square \% \) (Round to one decimal place as needed.)

Ask by Maxwell Morrison. in the United States
Feb 22,2025

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(a) 99.7% (b) 0.3% (c) 2.3%

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We are given a normally distributed variable X ~ N(525, 114). (a) The scores 183 and 867 correspond to 3 standard deviations below and above the mean, respectively:   525 – 3(114) = 183   525 + 3(114) = 867 Because about 99.7% of values lie within 3 standard deviations (the 68–95–99.7 rule), about 99.7% of scores fall between 183 and 867. (b) Since 99.7% are between 183 and 867, the percentage less than 183 or greater than 867 is 100% – 99.7% = 0.3%. (c) To find the percentage greater than 753, first calculate its z-score:   z = (753 – 525) / 114 = 228 / 114 = 2.0 Using the standard normal distribution:   P(Z < 2.0) ≈ 0.9772, so   P(Z > 2.0) = 1 – 0.9772 = 0.0228 or 2.28% Rounded to one decimal place, approximately 2.3% of test scores are greater than 753. Thus, the answers are: (a) 99.7% (b) 0.3% (c) 2.3%

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To find the percentage of standardized test scores greater than 753, we start with the mean (525) and the standard deviation (114). First, we need to calculate the z-score for the score of 753: \[ z = \frac{(X - \text{Mean})}{\text{Standard Deviation}} = \frac{(753 - 525)}{114} \approx 2.0 \] Now, using the z-score table or a calculator, we find that the cumulative percentage for a z-score of 2.0 is approximately 97.72%. This means that about 97.72% of scores fall below 753. To find the percentage of scores that are greater than 753, we subtract this value from 100%: \[ 100\% - 97.72\% = 2.28\% \] Thus, the percentage of standardized test scores greater than 753 is approximately **2.3%** when rounded to one decimal place. Have fun with statistical norms! Remember, when it comes to normal distributions, don't let standard deviations intimidate you; they’re just ways to show how spread out your data is! Additionally, if you're interested in diving deeper into statistics, consider checking out “The Elements of Statistical Learning” by Hastie, Tibshirani, and Friedman. It's a bit academic, but it’s packed with insights that make understanding data fun and engaging!

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