The average of 9 observations was 8, that of the 1st of 5 being 10 and that of the last 5 being 8. What was the 5th observation?
Options.
A) 18 B) 12 C) 15 D) 17 E) 19

Rationale: explanation : 1 to 9 = 8 * 9 = 72 1 to 5 = 5 * 10 = 50 5 to 9 = 5 * 8 = 40 5 th = 50 + 40 = 90 – 72 = 18 option a
Answer: A