Multiple choice

Mean of 70 values was calculated as 400, On rechecking it was discovered that 250 was wrongly copied as 355 .The correct mean is

  1. No change
  2. $401.5$
  3. $398.5$

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

Original sum = 70 * 400 = 28000. Correct sum = 28000 - 355 + 250 = 27895. Correct mean = 27895 / 70 = 398.5.

AI explanation

Using the formula for the arithmetic mean, the incorrect sum of the 70 values is 70 times 400, which equals 28000. To find the correct sum, subtract the wrongly copied 355 and add the correct value of 250, giving 28000 minus 355 plus 250, which equals 27895. Dividing this correct sum by 70 gives the correct mean of 398.5.

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