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Classes 0–20, 20–40, 40–60, 60–80 and 80–100 have frequencies 5, 9, f, 11 and 5, and the mean of the distribution is 51. Find f.

Competition practiceStatistics

A12
B8
C15
D10

Step-by-Step Solution

Class marks 10, 30, 50, 70, 90.

Σ f x = 1540 + 50 f, N = 30 + f .1540 + 50 f = 51 (30 + f) = 1530 + 51 f \Rightarrow f = 10

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Answer: D) 10

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