Multiple choice

The mean of a set of $20$ observation is $ 19.3$ . The mean is reduced by $ 0.5$ when a new observation is added to the set. The new observation is

  1. $19.8$
  2. $8.8$
  3. $9.5$
  4. $30.8$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Sum of 20 observations = 20 * 19.3 = 386. New sum of 21 observations = 21 * 18.8 = 394.8. New observation = 394.8 - 386 = 8.8.

AI explanation

The total sum of the original 20 observations is 20 multiplied by 19.3, which equals 386. When the new observation is added, the total number of observations becomes 21, and the new mean is 19.3 minus 0.5, equaling 18.8. The new total sum is therefore 21 multiplied by 18.8, which gives 394.8. The value of the new observation is the difference between the new sum and the old sum: 394.8 minus 386 equals 8.8.

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