Question

The class average on a math test was an 82 with a standard deviation of 5. If the 

Answer 1

Answer:

Option 3 and 4.

Step-by-step explanation:

The z score shows by how many standard deviations the raw score is above or below the mean. The z score is given by:

$z=\frac{x-\mu}{\sigma} \\\\where\ x=raw\ score,\mu=mean, \ \sigma=standard\ deviation$

Given that mean (μ) = 82, standard deviation (σ) = 5

1) For x = 74:

$z=\frac{x-\mu}{\sigma} \\\\z=\frac{74-82}{5} =-1.6$

Option 1 is incorrect

2) For x < 87

$z=\frac{x-\mu}{\sigma} \\\\z=\frac{87-82}{5} =1$

From the normal distribution table, P(x < 87) = P(z < 1) = 0.8413 = 84.13%

Option 2 is incorrect

3) For x = 95:

$z=\frac{x-\mu}{\sigma} \\\\z=\frac{95-82}{5} =2.6$

Option 3 is correct

4) For x < 77

$z=\frac{x-\mu}{\sigma} \\\\z=\frac{77-82}{5} =-1$

From the normal distribution table, P(x < 77) = P(z < -1) = 0.16 = 16%

Option 4 is correct

5) For x > 92

$z=\frac{x-\mu}{\sigma} \\\\z=\frac{92-82}{5} =2$

From the normal distribution table, P(x > 92) = P(z > 2) = 1 - P(z < -2) = 1 - 0.9772 = 0.0228 = 2.28%

Option 5 is incorrect