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Question
Calculate the mean of the scores of 20 students in a mathematics test:
| Marks | 10 – 20 | 20 – 30 | 30 – 40 | 40 – 50 | 50 – 60 |
| Number of students |
2 | 4 | 7 | 6 | 1 |
Solution
We first, find the class mark xi of each class and then proceed as follows.
| Marks | Class marks `(bb(x_i))` |
Frequency `(bb(f_i))` |
`bb(f_ix_i)` |
| 10 – 20 | 15 | 2 | 30 |
| 20 – 30 | 25 | 4 | 100 |
| 30 – 40 | 35 | 7 | 245 |
| 40 – 50 | 45 | 6 | 270 |
| 50 – 60 | 55 | 1 | 55 |
| `sumf_i = 20` | `sumf_ix_i = 700` |
Therefore, mean `(barx) = (sumf_ix_i)/(sumf_i)`
= `700/20`
= 35
Hence, the mean of scores of 20 students in mathematics test is 35.
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