Question

Given that z is a standard normal random variable, find z for each situation (to 2 decimals).

A. The area to the right of z is 001.
B. The area to the right of z is 0.045.
C. The area to the right of z is 0.05.
D. The area to the right of z is 0.2.

Answer 1

a) Z = 2.33

b) Z = 1.7

c) Z = 1.65.

d) Z = 0.84.

Explanation:

Z-score:

In a set with mean
`\mu` and standard deviation
`\sigma`, the zscore of a measure X is given by:

`Z = (X - \mu)/(\sigma)`

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X, which is also the area to the left of z. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X, which is also the area to the right of z.

A. The area to the right of z is 0.01.

Z has a pvalue of 1 - 0.01 = 0.99. So Z = 2.33.

B. The area to the right of z is 0.045.

Z has a pvalue of 1 - 0.045 = 0.955. So Z = 1.7

C. The area to the right of z is 0.05.

Z has a pvalue of 1 - 0.05 = 0.95. So Z = 1.65.

D. The area to the right of z is 0.2.

Z has a pvalue of 1 - 0.2 = 0.8. So Z = 0.84.