2018 · Q53
The arithmetic mean of 11 observations is 11. The arithmetic mean of the first 6 observations is 10.5 and the arithmetic mean of the last 6 observations is 11.5. What is the sixth observation?
Elementary MathematicsStatistics
- A10.0
- B10.5
- C11.0
- D11.5
Explanation
The sixth observation is counted in both partial means: 6(10.5) + 6(11.5) − 11(11) = 63 + 69 − 121 = 11.0, option (C).