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The following cumulative ('below') frequency table gives the marks of 85 students. Find the mean marks. Below 10: 5; Below 20: 9; Below 30: 18; Below 40: 29; Below 50: 45; Below 60: 60; Below 70: 70; Below 80: 78; Below 90: 83; Below 100: 85.

1. 48.41
2. 50.00
3. 52.35
4. 46.20

Correct answer: 48.41

Solution

Differencing the cumulative counts gives the class frequencies; the weighted mean of the class midpoints is about 48.41.

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