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T2.8. Which of the following is not correct about a standard Normal distribution?
(a) The proportion of scores that satisfy 0<z<1.5is 0.4332.
(b) The proportion of scores that satisfy z<-1.0is 0.1587.
(c) The proportion of scores that satisfy z>2.0is 0.0228.
(d) The proportion of scores that satisfy z<1.5is 0.9332.
(e) The proportion of scores that satisfyz>-3.0is 0.9938.

Short Answer

Expert verified

Option (e) is a conventional Normal distribution that is incorrect; the proportion of scores that fulfil z>-3.0 is0.9938.

Step by step solution

01

Given information

(a) The proportion of scores that satisfy 0<z<1.5 is 0.4332.
(b) The proportion of scores that satisfy z<-1.0 is 0.1587.
(c) The proportion of scores that satisfy z>2.0 is 0.0228.
(d) The proportion of scores that satisfy z<1.5 is 0.9332.
(e) The proportion of scores that satisfy z>-3.0 is 0.9938.

02

Explanation

(a) In the normal probability table in the appendix, the proportion of scores less than 0is shown in the row with 0.0and the column with .00.

P(z<0)=0.5000

In the normal probability table in the appendix, in the row with 1.5and in the column with .00, the fraction of scores less than 1.5is shown.

P(z<1.5)=0.9332

The difference between the proportions of scores to the left of two z-scores is the proportion of scores between the two z-scores.

localid="1649920681288" P(0<z<1.5)=P(z<1.5)-P(z<0)=0.93320.5000=0.4332

Hence, the proportion of scores that satisfy 0<z<1.5is 0.4332So, the given statement is correct.

Command Ti83/84-calculator: Normalcdf (0,1.5,0,1)

03

Explanation

(b) The proportion of scores lower than -1.0is given in the normal probability table in the appendix in the row with -1.0and in the column with .00
P(z<-1.0)=0.1587
Hence, the proportion of scores that satisfy z<-1.0is 0.1587. So, the given statement is correct.
Command Ti83/84-calculator: Normalcdf(-1E99,-1.0,0,1)

04

Explanation

(c) The proportion of scores lower than 2.0is given in the normal probability table in the appendix in the row with 2.0and in the column with .00
P(z<2.0)=0.9772
The total probability needs to be1, thus the probability to the right of 2.0is 1decreased by the probability to the left of 2.0
P(z>2.0)=1-P(z<2.0)=1-0.9772=0.0228

Hence, the proportion of scores that satisfyz>2.0is 0.0228. So, the given statement is correct.

Command Ti83/84-calculator: Normalcdf (2.0,1E99,0,1)

05

Explanation

(d) The proportion of scores lower than 1.5is given in the normal probability table in the appendix in the row with 1.5and in the column with .00
P(z<1.5)=0.9332
Hence, the proportion of scores that satisfy z<1.5is 0.9332. So, the given statement is correct.
Command Ti83/84-calculator: Normalcdf(-1E99,1.5,0,1).

06

Explanation

(e) The proportion of scores lower than -3.0is given in the normal probability table in the appendix in the row with -3.0and in the column with.00
P(z<-3.0)=0.0013
The total probability needs to be 1, hence the probability to the right of 2.0is 1decreased by the probability to the left of 2.0
P(z>-3.0)=1-P(z<-3.0)=1-0.0013=0.9987

Hence, the proportion of scores that satisfy z>-3.0is0.9987. So, the given statement is not correct (as 0.9987is different from

0.9938).

Command Ti83/84-calculator: Normalcdf(-3.0,1E99,0,1).

So, the option (e) is correct.

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