Question
Average of 15 observations calculated by a student was
70 but when he again went through his observations he realised that he took value of three observations as 50, 55 and 60 in place of 80, 41 and 72 respectively and also realised that total observations taken by him was 14. Find the original average of all observations taken by him.Solution
Sum of 15 observations = 15 × 70 = 1050 Original average = {1050 + (80 + 41 + 72) - (50 + 55 + 60)}/14 = 1078/14 = 77
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