The following table shows the marks scored by 140 students in an examination of a certain paper.
Marks: |
0−10 |
10−20 |
20−30 |
30−40 |
40−50 |
Number of students: |
20 |
24 |
40 |
36 |
20 |
Calculate the average marks by using all the three methods: direct method, assumed mean deviation and shortcut method.