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The mean and variance of eight numbers 3, 7, 9, 12, 13, 20, x, and y are 10 and 25 respectively. What is the value of (x * y) / 9?

1. 6
2. 7
3. 8
4. 9

Correct answer: 6

Solution

Setting up mean and variance equations gives x + y = 16 and x² + y² = 148. From these, xy = [(x+y)² - (x²+y²)] / 2 = (256 - 148) / 2 = 54. Therefore (xy)/9 = 54/9 = 6.

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