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Five observations from an experiment have mean 4 and variance 5.2. Three of the observations are 1, 2 and 6. Find the remaining two observations.

1. 2, 9
2. 5, 6
3. 4, 7
4. 3, 8

Correct answer: 4, 7

Solution

Let the two unknowns be a and b. Mean gives a + b = 11; variance gives a² + b² = 65, so a = 4, b = 7.

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