Multiple choice

The mean of 5 observations is 30. If the first four observations are 20, 25, 30 and 35, then find the last observation.

  1. 35

  2. 38

  3. 40

  4. 45

  5. na
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C Correct answer
Explanation

Sum of 5 observations = 5 * 30 = 150. Sum of first 4 = 20 + 25 + 30 + 35 = 110. Last observation = 150 - 110 = 40.

AI explanation

The formula for the mean is the sum of observations divided by the number of observations. The sum of all 5 observations must be 5 times 30, which is 150. The sum of the first four observations is 20 plus 25 plus 30 plus 35, equaling 110. Subtracting this from the total sum gives the last observation as 150 minus 110, resulting in 40.

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