What is the mean deviation about the arithmetic mean ?
For the next two (02) items that follow : The frequency distribution of marks obtained by 100 students in a certain subject is given below : <table border='1' cellpadding='6' cellspacing='0'> <tr><th>Marks</th><th>0-10</th><th>10-20</th><th>20-30</th><th>30-40</th></tr> <tr><td>No. of students</td><td>10</td><td>20</td><td>f</td><td>40</td></tr> </table>
- A. 5.5
- B. 6
- C. 6.5
- D. 8 ✓
Correct Answer: D. 8
Explanation
Total frequency is 100, so f = 100 - (10+20+40) = 30. Class marks are 5, 15, 25, 35. Mean = (50+300+750+1400)/100 = 25. Mean Deviation = \sum f_i|x_i - \text{mean}| / 100 = (10*20 + 20*10 + 30*0 + 40*10)/100 = 800/100 = 8.
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