Question
Average of 20 observations calculated by a student was
85 but when he again went through his observations he realised that he took value of three observations as 52, 60 and 55 in place of 90, 12 and 75 respectively and also realised that total observations taken by him was 19. Find the original average of all observations taken by him.Solution
Sum of 20 observations = 20 × 85 = 1700 Original average = {1700 + (90 + 12 + 75) - (52 + 60 + 55)}/19 = 1710/19 = 90
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