Name____________________________________
Practice: Percentage Under Normal Bell Curve
SOL: A2.T9
A normal distribution has a mean of 27 and a standard deviation of 5. Find the probability that a randomly selected xvalue from the distribution is in the given interval.
1.
Between 22 and 32
2.
Between 12 and 27
3.
Between 17 and 37
4.
A least 22
5.
At least 37
6.
At most 32
A normal distribution has a mean of 75 and a standard deviation of 10. Find the indicated probability for a randomly
selected x-value from the distribution.
7.
P ( x  70)
10.
The weights of adult male rhesus monkeys are normally distributed with a mean of 17 pounds and a standard
deviation of 3 pounds.
8.
P ( x  52)
9.
P ( x  78)
a. What is the probability that a randomly selected adult male rhesus monkey has a weight less than 14
pounds.?
b. What is the probability that a randomly selected adult male rhesus monkey has a weight less than 19
pounds?
c. What is the probability that a randomly selected adult male rhesus monkey has a weight greater than 12
pounds?
d. What is the probability that a randomly selected adult male rhesus monkey weights between 14 and 21
pounds?
A normal distribution has a mean of 125.8 and a standard deviation of 10.4. Find the indicated probability for a
randomly selected x-value from the distribution.
11.
P ( x  92.6)
12.
P( x  153.7)
13.
P(99.8  x  112.3)
14.
Pat and Chris both took a spatial abilities test which is normally distributed with a mean of 80 and a standard
deviation of 8. Pat scores a 76 and Chris scored a 94. What percent of individuals would score between Pat
and Chris?
15.
A fifth grader takes a standardized achievement test (mean = 125, standard deviation = 15) and scores a 148.
What is the child’s percentile rank?
16.
A patient recently diagnosed with Alzheimer’s disease takes a cognitive abilities test and scores a 45. The mean
on this test is 52 and the standard deviation is 5. What is the patient’s percentile rank?
17.
The Welcher Adult Intelligence Test Scale is composed of a number of subtests. On one subtest, the raw scores
have a mean of 35 and a standard deviation of 6. Assuming these raw scores form a normal distribution:
a) What number represents the 65th percentile (what number separates the lower 65% of the distribution)?
b) What number represents the 90th percentile?
c) What is the probability of getting a raw score between 28 and 38?
d) What is the probability of getting a raw score between 41 and 44?
18.
The blood pressure of adult males is normally distributed with a mean of 125mm/hg and a standard
deviation of 8.
a) What is the minimum blood pressure of the 50% with the highest blood pressures?
b) What is the minimum blood pressure of the 30% with the highest blood pressures?
c) What is the maximum blood pressure of the 30% with the lowest blood pressures?
d) What is the minimum blood pressure of the 20% with the highest blood pressures?
19.
Scores on the SAT form a normal distribution with   500 and
necessary to be in the top 15% of the SAT distribution?
  100 .What is the minimum score