Download Normal Distribution Review #1

Statistics
Review for Normal Distribution Quiz #1
1. The shelf life of a particular dairy product is normally distributed with a mean of 12
days and a standard deviation of 3 days.
a) About what percent of the products last between 9 and 15 days?
b) About what percent of the products last between 12 and 15 days?
c) About what percent of the products last 6 days or less?
d) About what percent of the products last 15 or more days?
2. Find the area under the standard normal curve to the right of z = -1.25
3. Find the area under the standard normal curve between z = -1.25 and z = 1.25
4. Scores on a standardized test are normally distributed with a mean of 100 and a
standard deviation of 12. An individual's test score is found to be 125. Find the z-score
corresponding to this value.
5. For a standard normal curve, find the z-score that separates the bottom 30% from the
top 70%.
6. Find the z-scores for which 80% of the distribution's area lies between -z and z.
7. A normal distribution has a mean of 20 and a standard deviation of 4. Find the
percentile rank for a data value of 17 ( i.e. find the percentage of data values that are
below the data value of 17.
8. Birth weights of infants at a local hospital have a normal distribution with a mean of
110 oz. and a standard deviation of 15 oz.
a.
What percentage of infants weigh between 100 oz. and 125 oz. at birth?
b. What percentage of infants weigh more than 160 oz. at birth? (that’s 10 lbs)
c.
What birth weight corresponds to the 65th percentile?
9. The mean cholesterol level in children is 175 mg/dL with standard deviation 35
mg/dL. Assume this level varies from child to child according to an approximate normal
distribution.
a. What percentage of children have a cholesterol level above 200 mg/dL?
b. How high are the levels for the highest 2% of all children?
10. Wingspans of adult herons have approximate normal distribution with mean 125 cm
and standard deviation 12 cm.
a. What proportion of herons have wingspan more than 140 cm?
b.
What is the median wingspan?
c.
What are the first and third quartiles of the wingspans? (25% of all herons have
wingspan less than the first quartile; 25% have wingspan more than the third
quartile.) Use these to obtain the IQR for heron wingspans.