NumericalModerate3 marks
If the mean of the following distribution is 24, find the value of ‘a’.
Topic: Mean / median / mode / quartiles
Previous-year question practice database
Answer
Exam answer
| Marks | f | Class mark x | fx |
|---|---|---|---|
| 0–10 | 7 | 5 | 35 |
| 10–20 | a | 15 | 15a |
| 20–30 | 8 | 25 | 200 |
| 30–40 | 10 | 35 | 350 |
| 40–50 | 5 | 45 | 225 |
Σf = 30+a Σfx = 810+15a.
Given mean = 24: 24 = (810+15a)/(30+a)
720+24a = 810+15a 9a = 90 a = 10.
Answer: a=10.
Explanation
Use mean = Σfx/Σf and solve for the unknown frequency a.
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