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Suppose a normally distributed set of data has a mean of 108 and a standard deviation of 12. Use the 68-95-99.7 Rule to determine the percent of scores in the data set expected to be below a score of 120. Give your answer as a percent and include as many decimal places as the 68-95-99.7 Rule dictates.

Caution: Using tables or Excel for this may produce a wrong answer. Use the 68-95-99.7 Rule.

Answer :

By using the 68-95-99.7 Rule, the percent of scores in the data set that are expected to be below a score of 120 is 84.13%.

What is the Empirical Rule?

In Mathematics, the Empirical Rule is sometimes referred to as the 68-95-99.7 rule and it can be defined as a statistical rule which states that:

  1. The middle 68% of a normal distribution would be within 1 standard deviation of its mean i.e between μ - σ and μ + σ.
  2. The middle 95% of a normal distribution would be within 2 standard deviations of its mean i.e between μ - 2σ and μ + 2σ.
  3. The middle 99.7% of a normal distribution would be within 3 standard deviations of its mean i.e between μ - 3σ and μ + 3σ.

At the middle 68% of the normal distribution, we have the following standard score:

μ - σ = 108 - 12 = 96.

μ - σ = 108 + 12 = 120.

Where:

  • μ is the sample mean.
  • x is the score.
  • σ is the standard deviation.

At the middle 95% of the normal distribution, we have:

μ - σ = 108 - 2(12) = 84.

μ - σ = 108 + 2(12) = 132.

At the middle 99.7% of the normal distribution, we have:

μ - σ = 108 - 3(12) = 72.

μ - σ = 108 + 3(12) = 144.

Now, we can determine the percent (P) of scores in the data set that are expected to be below a score (x) of 120;

P(x < 120) = P((x - μ)/σ < (120 - 108)/12)

P(x < 120) = P((x - μ)/σ < 12/12)

P(x < 120) = P(z < 1)

P(x < 120) = 0.8413

P(x < 120) = 84.13%

Read more on Empirical Rule here: brainly.com/question/14824525

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