STANDARD NORMAL DISTRIBUTION

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# STANDARD NORMAL DISTRIBUTION - PowerPoint PPT Presentation

STANDARD NORMAL DISTRIBUTION. All normal distributions are same when standardized Find areas under normal curve from table that gives areas under curve for standard normal distribution

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STANDARD NORMAL DISTRIBUTION
• All normal distributions are same when standardized
• Find areas under normal curve from table that gives areas under curve for standard normal distribution
• table tells us proportions of values that lie above or below a certain distance from the mean (standard deviations) for any standardized distribution
• THE STANDARD NORMAL TABLE
• TABLE A
STANDARD NORMAL TABLE
• The table entry for each value z is the area under the curve to the left of z.

Picture on page 57

STANDARD NORMAL DISTRIBUTION

3.10 Use table A to find the proportion of observations from a standard normal distribution that satisfies each of the following statements. In each case, sketch a standard normal curve and shade the are under the curve that is the answer to the question.

• Z < 2.85
• Z > 2.85
• Z > -1.66
• -1.66 < z < 2.85
STANDARD NORMAL DISTRIBUTION

3.11 An important measure of the performance of a locomotive is its “adhesion” which is the locomotive’s pulling force as a multiple of its weight. The adhesion of one 4400-horspower diesel locomotive model varies in actual use according to a normal distribution with mean 0.37 and standard deviation of 0.04.

• What proportion of adhesions measured in use are higher than 0.40?
• What proportion of adhesions are between 0.40 and 0.50?
• Improvements in the locomotive’s computer controls change the distribution of adhesion to a normal distribution with mean 0.41 and standard deviation of 0.02. Find the proportions in (a) and (b) after this improvement.
STANDARD NORMAL DISTRIBUTION

3.12 Use Table A to find the value z of a standard normal variable that satisfies each of the following conditions. (Use the value of z from table A that comes closest to satisfying the condition). In each case, sketch a standard normal curve with your value of z marked on the axis

• The point z with 25% of the observations falling below it.
• The point z with 40% of the observations falling above it.
STANDARD NORMAL DISTRIBUTION

3.13 Scores on the Wechler Adult Intelligence Scale are approximately normally distributed with mean of 100 and standard deviation of 15.

• What IQ scores fall in the lowest 25% of the distribution?
• How high an IQ score is needed to be in the highest 5%?