Answer:
a. 0.4129 = 41.29% of the bank's Visa cardholders pay more than 29 dollars in interest.
b. 0.1867 = 18.67% of the bank's Visa cardholders pay more than 35 dollars in interest.
c. 0.0742 = 7.42% of the bank's Visa cardholders pay less than 14 dollars in interest.
d. An interest payment of $35.2 is exceeded by only 18% of the bank's Visa cardholders.
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 z-score 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 p-value, we get the probability that the value of the measure is greater than X.
Mean of 27 dollars and a standard deviation of 9 dollars.
This means that
A. What proportion of the bank's Visa cardholders pay more than 29 dollars in interest?
This is 1 subtracted by the p-value of Z when X = 29, so:
has a p-value of 0.5871.
1 - 0.5871 = 0.4129
0.4129 = 41.29% of the bank's Visa cardholders pay more than 29 dollars in interest.
B. What proportion of the bank's Visa cardholders pay more than 35 dollars in interest?
This is 1 subtracted by the p-value of Z when X = 35, so:
has a p-value of 0.8133.
1 - 0.8133 = 0.1867
0.1867 = 18.67% of the bank's Visa cardholders pay more than 35 dollars in interest.
C. What proportion of the bank's Visa cardholders pay less than 14 dollars in interest?
This is the p-value of Z when X = 14. So
has a p-value of 0.0742.
0.0742 = 7.42% of the bank's Visa cardholders pay less than 14 dollars in interest.
D. What interest payment is exceeded by only 18% of the bank's Visa cardholders?
This is the 100 - 18 = 82nd percentile, which is X when Z has a p-value of 0.82, so X when Z = 0.915.
An interest payment of $35.2 is exceeded by only 18% of the bank's Visa cardholders.