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WAEC Mathematics 2019 Paper

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Question : 41

Total: 50

Calculate the variance of 2, 4, 7, 8 and 9

7.2
6.8
3.5
2.6

Solution:

Concept:

Variance is the average of the squared deviations of each value from the mean.

Explanation:

Data set:

2, 4, 7, 8, 9

.

Mean:

\overline{x} = \frac{2+4+7+8+9}{5} = \frac{30}{5} = 6

.

Deviations from the mean:

2-6=-4

,

4-6=-2

,

7-6=1

,

8-6=2

,

9-6=3

.

Squared deviations:

16, 4, 1, 4, 9

.

Sum of squared deviations:

\sum (x-\overline{x})^2 = 16+4+1+4+9 = 34

.

Variance:

\frac{\sum (x-\overline{x})^2}{n} = \frac{34}{5} = 6.8

.

Answer:

B.

6.8

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