Multiple choice

The average of n observations is 40. If one observation of value 80 is added, then the average of all the observations is 41. What is the value of n?

  1. 40

  2. 39

  3. 38

  4. 43
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initial sum of n observations is 40n. After adding 80, the new sum is 40n + 80, and the number of observations is n + 1. The new average is (40n + 80) / (n + 1) = 41. Solving for n: 40n + 80 = 41n + 41, so n = 39.

AI explanation

The original total sum of the observations is 40n. Adding one observation of value 80 creates a new sum of 40n + 80, and this is divided by n + 1 observations to equal the new average of 41. Setting up the equation 40n + 80 = 41(n + 1) yields 40n + 80 = 41n + 41. Solving for n gives a value of 39.

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