# Statistics - Value - Probability

1. What value represents the 25th percentile?

2. A normal distribution has a mean of 80 and a standard deviation of 14. Determine the value above which 80% of the values will occur.

3. A normal population has a mean of 75 and a standard deviation of 5. You select a sample of 40. Compute the probability the sample mean is:

a) Less than 74

b) Between 74 and 76

c) Between 76 and 77

d) Greater than 77

#### Solution Preview

...th percentile corresponds to z = -0.6745

(2) m = 80, s = 14

P(z > a) = 0.80 for a = -0.8416

x = m + z * s = 80 - 0.8416 * 14 = 68.22

(3) m = 75, s = 5, n ...