Multiple choice

Mean of 50 values was calculated as 122 On checking it was discovered that observations 40, 50 and 60 were wrongly copied as 20, 25 and 55 The correct means is

  1. 172

  2. 122

  3. 123

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Original sum = 50 * 122 = 6100. Wrong values sum = 20 + 25 + 55 = 100. Correct values sum = 40 + 50 + 60 = 150. Difference = +50. Correct sum = 6150. Correct mean = 6150 / 50 = 123.

AI explanation

Using the arithmetic mean formula, the incorrect total sum of the 50 values is 50 times 122, which equals 6100. The correct sum is found by subtracting the wrong values and adding the correct ones: 6100 minus 20 minus 25 minus 55 plus 40 plus 50 plus 60, which equals 6150. Dividing this correct sum by 50 gives the correct mean of 123.

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