The amount of time all students in a very large undergraduate statistics course take to complete an examination is distributed continuously and normally. The probability a student selected at random takes at least 55.50 minutes to complete the examination equals 0.6915. The probability a student selected at random takes no more than 71.52 minutes to complete the examination equals 0.8997. a) Determine the value for the mean (u) of the associated distribution
b) Determine the value for the standard deviation (o) of the associated distribution.

a) The mean is

b) The standard deviation is

Step-by-step explanation:

Normal Probability Distribution:

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

In a set with mean and standard deviation , the zscore of a measure X is given by:

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 pvalue, we get the probability that the value of the measure is greater than X.

The probability a student selected at random takes at least 55.50 minutes to complete the examination equals 0.6915.

This means that when X = 55.5, Z has a pvalue of 1 - 0.6915 = 0.3085. This means that when

So

The probability a student selected at random takes no more than 71.52 minutes to complete the examination equals 0.8997.

This means that when X = 71.52, Z has a pvalue of 0.8997. This means that when

So

Since we also have that

Question

The mean is

The standard deviation is

square root of 36/6 = 2.449489743

square root of 16/6 = 1.632993162

square root of 6 = 2.449489743

the answer is square root of 16/6 because the square root of 36/6 is the same answer as square root of 6 = 2.449489743