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What is the quartile deviation for the data set 12, 7, 15, 10, 16, 17, 25?

1. 4.5
2. 13.5
3. 9
4. 3.5

Correct answer: 3.5

Solution

Sort the data: 7,10,12,15,16,17,25 (n=7). Q1 is the (n+1)/4 = 2nd value = 10; Q3 is the 3(n+1)/4 = 6th value = 17. Quartile deviation = (Q3 - Q1)/2 = (17 - 10)/2 = 3.5.

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