Average of 9 observations was 9, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?

– by 0

A. 12
B. 16
C. 9
D. 23

1 to 9 = 9 * 9 = 81

1 to 5 = 5 * 10 = 50

5 to 9 = 5 * 8 = 40

5th = 50 + 40 = 90 – 81 = 9

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