Question

1.

Scores on an aptitude test form a normal distribution with a mean of 140 and a standard deviaition of 12. Find the percent that score between 131 and 155.

Group of answer choices

12.10%

22.66%

32.44%

66.78%

10.56%

2.

The scores of students on a standardized test form a normal distribution with a mean of 140 and a standard deviaition of 12. If 36000 students took the test, how many scored above 149?

Group of answer choices

9634

7922

7846

8158

6542

Answer 1

1)

P(131 < x < 155) = P[(131 - 140)/ 12) < (x - ) /  < (155 - 140) / 12) ]

= P(-0.75 < z < 1.25)

= P(z < 1.25) - P(z < -0.75)

= 0.6678

= 66.78%

2)

P(x > 149) = 1 - P(x < 149)

= 1 - P[(x - ) / < (149 - 140) / 12]  

= 1 - P(z < 0.75)

= 0.2266

Score = 0.2266 * 0.36000 = 8158