The youngest of 4 children has siblings who are 2, 7, and 11 years older than she is. If the average (arithmetic mean) age of the 4 siblings is 25, what is the age of the youngest sibling?  Select:
A) 17 B) 18 C) 19 D) 20 E) 21

Rationale: "x + ( x + 2 ) + ( x + 7 ) + ( x + 11 ) = 100 4 x + 20 = 100 4 x = 80 x = 20 the answer is d ."
Answer: D