Question

Use the cumulative normal distribution table to find the z-scores thqt bound the middle of 68% of theje area under the stanrard normal curve

Answer 1

Z scores between -0.995 and 0.995 bound the middle 68% of the area under the stanrard normal curve

Explanation:

Normal Probability Distribution:

Problems of normal distributions can be solved using the z-score formula.

In a set with mean
`\mu` and standard deviation
`\sigma`, the z-score of a measure X is given by:

`Z = (X - \mu)/(\sigma)`

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.

Middle 68%

Between the 50 - (68/2) = 16th percentile and the 50 + (68/2) = 84th percentile.

16th percentile:

X when Z has a pvalue of 0.16. So X when Z = -0.995

84th percentile:

X when Z has a pvalue of 0.84. So X when Z = 0.995.

Z scores between -0.995 and 0.995 bound the middle 68% of the area under the stanrard normal curve