Multiple choice

The mean of certain number of observations is 46. If four observation whose main is 52 are removed, the mean becomes 44.5. The original number of observation is:

  1. 35

  2. 20

  3. 15

  4. 12
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If the original number of observations is n, the original total is 46n. Removing four observations with mean 52 removes 208, leaving 44.5(n - 4). Solving 46n - 208 = 44.5(n - 4) gives n = 20.

AI explanation

Let the original number of observations be n, so the original total sum is 46n. The sum of the four removed observations is 4 times 52, which is 208. Setting up the equation for the new mean, (46n - 208) divided by (n - 4) equals 44.5, and solving for n gives 46n - 208 = 44.5n - 178. This simplifies to 1.5n = 30, so the original number of observations is 20.

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