The following table shows the marks scored by 80 students in an examination:
Marks
Less than 5
Less than 10
Less than 15
Less than 20
Less than 25
Less than 30
Less than 35
Less than 40
Number of students
3
10
25
49
65
73
78
80
Calculate the mean marks correct to 2 decimal places.
Answers
18.56 is Mean marks scored by 80 students in an examination
Step-by-step explanation:
Marks cf f Mean Class u =(mean - 17.5)/5 u*f
0 - 5 3 3 2.5 -3 -9
5 - 10 10 7 7.5 -2 -14
10 - 15 25 15 12.5 -1 -15
15 - 20 49 24 17.5 0 0
20 - 25 65 16 22.5 1 16
25 - 30 73 8 27.5 2 16
30 -35 78 5 32.5 3 15
35 - 40 80 2 37.5 4 8
80 17
Mean = 17.5 + 5 * 17/80
= 17.5 + 1.06
= 18.56
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Step-by-step explanation:
Marks. cumulative frequency. frequency. class mark. class mark x frequency
0 to 5 3. 3. 2.5. 7.5
5 to 10. 10. 7. 7.5. 52.5
10 to 15. 25. 15. 12.5. 187.5
15 to 20. 49. 24. 17.5. 420
20 to 25. 65. 16. 22.5. 360.
25 to 30. 73. 8. 27.5. 220
30 to 35. 78. 5. 32.5. 162.5.
35 to 40. 80. 2. 37.5. 75.
+. =. 80*. + = 1485*
mean x = addition of cumulative frequency and class mark / addition of frequency
= 1485/80
= 18.56
* addition of cumulative frequency and class mark
*addition of frequency
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