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NTA Abhyas JEE Main2020MathematicsStatisticsPractice

Let one observation equal to the mean is added to n observations. If the variance changes from 78 to 72 , then n is equal to

Correct answer

12

Step-by-step solution

Adding mean to the observations does not change the value of ∑ x i - x - 2 , hence, ∑ i = 1 n x i - x - 2 n ∑ i = 1 n + 1 x i - x - 2 n + 1 = 78 72   ⇒ n + 1 n = 78 72 ⇒ n = 12

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