Question

Use a statistics calculator to find the area, in decimal form, rounded to four places after the decimal, under the (standard) Normal histogram and... (a) ...to the left of 1.8. (b) ...to the right of 2.4. (c) ...between 1.8 and 2.4.

Answer 1

a) 0.9641.

b) 0.0082

c) 0.0277

Explanation:

Normal Probability Distribution:

Problems of normal distributions can be solved using the z-score formula.

In a set with mean
`\mu` and standard deviation
`\sigma`, the z-score 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. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.

(a) ...to the left of 1.8.

p-value of Z = 1.8, which, looking at the z-table, is of 0.9641.

(b) ...to the right of 2.4.

1 subtracted by the p-value of Z = 2.4.

Looking at the z-table, Z = 2.4 has a p-value of 0.9918.

1 - 0.9918 = 0.0082, which is the answer.

(c) ...between 1.8 and 2.4.

p-value of Z = 2.4 subtracted by the p-value of Z = 1.8.

From itens a and b, we have both. So

0.9918 - 0.9641 = 0.0277