The average of 15 numbers is 7. If the average of the first 8 numbers be 6.5 and

Question

The average of 15 numbers is 7. If the average of the first 8 numbers be 6.5 and the average of last 8 numbers be 9.5, then the middle number is

Options:

A . 21

B . 18

C . 23

D . 20

Answer: Option C
Answer: (c)Using Rule 1, The middle number = 8 × 6.5 + 8 × 9.5 – 15 × 7 = 52 + 76 – 105 = 128 – 105 = 23

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