Average of 28 observations is 53. Average of first 11 observations is 54. Average of last 18 observations is 52.5. What is the value of 11th observation?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 55.
Total sum of 28 observations = 28 × 53 = 1484
Sum of first 11 observations = 11 × 54 = 594
Sum of last 18 observations = 18 × 52.5 = 945
Sum of first 11 observations + Sum of last 18 observations- 11th observation = Total sum of 28 observations
⇒ 594 + 945 - x11 = 1484
⇒ 1539 - x11 = 1484
⇒ x11 = 1539 - 1484 = 55