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The mean marks of 30 students in a class is 58.5. Later on it was found that 75 was wrongly recorded as 57. Find the correct them.

Correct answer: D. 59.1Everyday Science Quiz

  • A. 57.4
  • B. 57.5
  • C. 58.9
  • D. 59.1Everyday Science Quiz

Explanation

The recorded total is 30 students x 58.5 marks = 1755 marks. Correcting 57 marks to 75 marks adds 18 marks, so the new average is (1755 + 18) marks ÷ 30 students = 59.1 marks. The likely mistake is option c, which may result from adding 18 marks directly to the average instead of distributing it among 30 students.

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An average represents the total of a set of values divided by the number of values, and a weighted average gives different importance to different groups. Problems involve missing values, combined averages, replacement of observations, and changes in the average, so the total and count must be tracked separately.

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