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If the standard deviation of the numbers 2, 3, a and 11 is 3.5, then which of the following is true ?

1. 3a 2 – 26a + 55 = 0
2. 3a 2 – 32a + 84 = 0
3. 3a 2 – 34a + 91 = 0
4. 3a 2 – 23a + 44 = 0

Correct answer: 3a 2 – 32a + 84 = 0

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