Question

1500 test scores were normally distributed with a mean of 82 and a standard deviation of 7.

How many people scored more than 90?

Answer 1

Solution:

Given: 1500 test scores were normally distributed with a mean of 82 and a standard deviation of 7.

thus and

We have to find number of people scored more than 90.

thus first find:

P(X > 90) =........?

Find z score for x = 90

thus we get:

Look in z table for z = 1.1 and 0.04 and find corresponding area.

P( Z< 1.14) = 0.8729

thus

thus

Number of people scored more than 90 = N * P( X > 90)

Number of people scored more than 90 = 1500 * 0.1271

Number of people scored more than 90 = 190.65

Number of people scored more than 90 = 191