Question

Use the normal distribution bell curve.

The mean for a set of scores is 100 and the standard deviation is 7.5. Find the probability that a randomly selected score is between
a. 85 and 100.
b. between 85 and 115
c. less than 100

Answer 1

The IQ test scores are Normally distributed with mean 100 and standard deviation 15.

Let X be the IQ test score of person.

We have to find the probability that person would score between 85 and 115 is

P(85 < X < 115) =

= P(-1 < Z < 1)

= P(Z < 1) - P(Z < -1)

= 0.8413 - 0.1587

P(85 < X < 115) = 0.6826

The probability that a person would score between 85 and 115 is 0.6826

Explanation: