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    Question

    Average of 10 observations calculated by a student was

    60 but when he again went through his observations he realised that he took value of three observations as 62, 54 and 50 in place of 86, 40 and 70 respectively and also realised that total observations taken by him was 9. Find the original average of all observations taken by him.
    A 77 Correct Answer Incorrect Answer
    B 72 Correct Answer Incorrect Answer
    C 70 Correct Answer Incorrect Answer
    D 78 Correct Answer Incorrect Answer

    Solution

    Sum of 10 observations = 10 × 60 = 600 Original average = {600 + (86 + 40 + 70) - (62 + 54 + 50)}/9 = 630/9 = 70

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