Single correct option
The average of 11 numbers is 36. The average of the first six numbers is 32 and that of the last six numbers is 41. What is the sixth number?
- A. 38
- B. 40
- C. 42
- D. 44
Show answer and solution
Answer: (C) 42
The sixth number belongs to both the 'first six' and the 'last six'.
Sum of first six + sum of last six = 6 × 32 + 6 × 41 = 192 + 246 = 438.
Sum of all eleven = 11 × 36 = 396.
The excess 438 − 396 = 42 is the sixth number, which was counted twice.
Sum of first six + sum of last six = 6 × 32 + 6 × 41 = 192 + 246 = 438.
Sum of all eleven = 11 × 36 = 396.
The excess 438 − 396 = 42 is the sixth number, which was counted twice.
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