JEE Mains · Maths · STD 11 - 13. statistics
If the mean of the data
| Class | \(5-10\) | \(10-15\) | \(15-20\) | \(20-25\) | \(25-30\) | \(30-35\) |
|---|---|---|---|---|---|---|
| Frequency | \(2\) | \(k\) | \(28\) | \(54\) | \(k+1\) | \(5\) |
is \(21\), then \(k\) is one of the roots of the equation :
- A \(2x^2 - 23x - 10 = 0\)
- B \(4x^2 - 35x + 24 = 0\)
- C \(2x^2 - 19x - 10 = 0\)
- D \(2x^2 - 35x + 98 = 0\)
Answer & Solution
Correct Answer
(C) \(2x^2 - 19x - 10 = 0\)
Step-by-step Solution
Detailed explanation
The class marks (mid-points) \(x_i\) for the given classes are \(7.5, 12.5, 17.5, 22.5, 27.5, 32.5\). The sum of the frequencies is: \(\sum f_i = 2 + k + 28 + 54 + (k + 1) + 5 = 2k + 90\) The sum of the products \(f_i x_i\) is:…
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