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Here are the IQ scores of 10randomly chosen fifth-grade students:

Which of the following statements about this data set is not true?

a. The student with an IQ of 96is considered an outlier by the 1.5IQRrule.

b. The five-number summary of the 10IQ scores is 96,118,123.5,130,145.

c. If the value 96were removed from the data set, the mean of the remaining 9IQ scores would be greater than the mean of all 10IQ scores.

d. If the value 96were removed from the data set, the standard deviation of the remaining 9IQ scores would be less than the standard deviation of all 10IQ scores.

e. If the value 96were removed from the data set, the IQR of the remaining 9IQ scores would be less than the IQR of all 10IQ scores.

Short Answer

Expert verified

The correct option is (e).

Step by step solution

01

Step 1. Given information

Given IQ score:

145,139,126,122,125,130,96,110,118,118

02

Step 2. Explanation

For option (a), order the data values from smallest to largest:

96,110,118,118,122,125,126,130,139,145

The median is the middle value of the data. And since the number of data is even then:

M=Q2=122+1252=2472=123.5

The first quartile is the median of the data values below the median i.e.

Q1=118

The third quartile is the median of the data values above the median i.e.

Q3=130

Now, the interquartile range will be:

IQR=Q3-Q1=130-118=12

Outliers are observations that are more than 1.5times the IQR above Q3orbelowQ1.

Q3+1.5IQR=130+1.5(12)=148Q1-1.5IQR=118-1.5(12)=100

Since96 lies below 100,96 is considered an outlier by the1.5 times interquartile range and thus the option (a) is true.

03

Step 3. Explanation

For option(b), the five summary consists of the minimum, first quartile, median, third quartile and the maximum, which are all the same thus the option (b) is true.

04

Step 4. Explanation

For option (c), 96is the smallest value in the data set. We then expect the mean to increase if96 is removed from the data set, as the centre of the data will become higher when the minimum is removed and thus, option (c) is true.

05

Step 5. Explanation

For option (d), the standard deviation measures the amount of variation or the spread of the data set. 96is the smallest value in the data set. We then expect the standard deviation to increase if96 is removed from the data set, as the spread decrease when the minimum is removed and thus, option (d) is true.

06

Step 6. Explanation

For option (e), 96is the smallest value in the data set and from part (a) we know that96 is an outlier. We then expect the IQR to not be affected if 96is removed from the data as the IQR should not be influenced by the outlier and thus option (e) is not true.

Thus, we will select the option (e) as correct answer.

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