Multiple choice

The average of 11 observations is 78. If the average of first six results is 69 and that of the last six is 82 marks, then the sixth observation is -

  1. 54

  2. 48

  3. 40

  4. 45

  5. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let the 11 observations be a1,a2,...,a11. Total sum = 11×78 = 858. Sum of first 6 = 6×69 = 414. Sum of last 6 = 6×82 = 492. The 6th observation is counted in both sums. So a6 = (414 + 492) - 858 = 906 - 858 = 48. Option B is correct.

Keep practicing — related questions