Multiple choice

The mean of 12 observations is 15. One more observation is included and the new mean becomes 16. The 13th⁴ observation is

  1. 20

  2. 24

  3. 28

  4. 26
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C Correct answer
Explanation

Total sum of 12 observations = 12 * 15 = 180. Total sum of 13 observations = 13 * 16 = 208. The 13th observation = 208 - 180 = 28.

AI explanation

The total sum of the initial 12 observations is 12 multiplied by 15, which equals 180. Let the 13th observation be x; the new mean for the 13 observations is calculated as (180 + x) divided by 13, which equals 16. Multiplying both sides by 13 gives 180 + x = 208, and subtracting 180 from 208 reveals that the 13th observation is 28.

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