Question

1. Use Excel to answer the following. In each question, find the blank to make the statement true. Note that Z represents we are using the standard normal distribution. Note: Round your answers to two decimal places. A) P(Z < -0.69) = B) P(Z > 1.84) = C) P(Z > )= 0.921 D) P(Z < ) = 0.61 2. Use Excel to answer the following. In each question, find the blank to make the statement true. In this example assume we have a variable X that is distributed normally with mean 30 and standard deviation 6. Note: Round your answers to two decimal places. A) P(X < 28.40) = B) P(X > 39.30) = C) P(X > )= 0.043 D) P(X < ) = 0.086

Answer 1

1. A: 0.25; B: 0.03; C: 1.41; D: -0.28

2. A: 0.39; B: 0.06; C: 40.30; D: 21.81

Explanation:

For CDF lookups, we used the Excel NORMDIST(x, mean, stdev, TRUE) function. For inverse CDF lookups, we used the NORMINV(x, mean, stdev) function.

Each of these functions works with the area under the curve from -∞ to x, so for cases where we're interested in the upper tail, we subtract the probability from 1, or subtract the x value from twice the mean.

For question 1, we computed the Z values in each case. The NORMDIST function works directly with x, mean, and standard deviation, so does not need the z value.