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WAEC Mathematics 2018 Paper

Question : 27

Total: 50

Find the inter-quartile range of 1, 3, 4, 5, 8, 9, 10, 11, 12, 14, 16

Solution:

Concept:

For an ordered data set, the inter-quartile range is

Q_3 - Q_1

, where

Q_1

and

Q_3

are found using their positions:

\frac{1}{4}(N+1)

and

\frac{3}{4}(N+1)

Explanation:

The data is already arranged in ascending order:

1, 3, 4, 5, 8, 9, 10, 11, 12, 14, 16

Here,

N = 11

Position of

Q_1 = \frac{1}{4}(11+1) = \frac{12}{4} = 3

The third value is

4

, so

Q_1 = 4

Position of

Q_3 = \frac{3}{4}(11+1) = \frac{36}{4} = 9

The ninth value is

12

, so

Q_3 = 12

Therefore, inter-quartile range =

Q_3 - Q_1 = 12 - 4 = 8

Answer:

8

(Option C).

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