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Question
The marks obtained by a set of students in an examination all given below:
| Marks | 5 | 10 | 15 | 20 | 25 | 30 |
| Number of students | 6 | 4 | 6 | 12 | x | 4 |
Given that the mean marks of the set of students is 18, Calculate the numerical value of x.
Solution
Calculation of Mean :
| Marks (x) | Number of students (f) | fx |
| 5 | 6 | 30 |
| 10 | 4 | 40 |
| 15 | 6 | 90 |
| 20 | 12 | 240 |
| 25 | x | 25x |
| 30 | 4 | 120 |
| `sumf = 32 + x` | `sumfx = 520 + 25x` |
∴ Mean = `(sumfx)/(sumf)`
∴ 18 = `(520 + 25x)/(32 + x)`
⇒ 576 + 18x = 520 + 25x
⇒ 7x = 56
⇒ x = 8.
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