The average of 6 observations is 15. A new observation is included and the new average is decreased by 1. The seventh observation is?  Choices:  A) 1  B) 8  C) 5  D) 6  E) 7

Rationale: "let seventh observation = x . then , according to the question we have = > ( 90 + x ) / 7 = 14 = > x = 8 hence , the seventh observation is 8 answer : b"
Answer: B