Class interval 1 - 5 6 - 10 11 - 15 16 - 20 21...

JAMB 1994

Class interval	1 - 5	6 - 10	11 - 15	16 - 20	21 - 25
Frequency	6	15	20	7	2

Estimate the median of the frequency distribution above

A. 10\(\frac{1}{2}\)
B. 11\(\frac{1}{2}\)
C. 12
D. 13

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Correct Answer: Option C

Explanation

Median = L + [\(\frac{\frac{N}{2} - f}{fm}\)]h

N = Sum of frequencies

L = lower class boundary of median class

f = sum of all frequencies below L

fm = frequency of modal class and

h = class width of median class

Median = 11 + [\(\frac{\frac{50}{2} - 21}{20}\)]5

= 11 + (\(\frac{25 - 21}{20}\))5

= 11 + (\(\frac{(4)}{20}\))

11 + 1 = 12