A cricketer whose bowling average is 12.4 runs per wicket takes 5 wickets for 26 runs and thereby decreases his average by 0.4. The number of wickets taken by him till the last match was:  Choose the correct choice from the following options
A) 64  B) 72  C) 80  D) 85  E) none of the above

Rationale: "let the number of wickets taken till the last match be x . then , 12.4 x + 26 / x + 5 = 12 ⇒ 12.4 x + 26 = 12 x + 60 ⇒ 0.4 x = 34 ⇒ x = 34 ⁄ 0.4 = 340 ⁄ 4 = 85 . answer d"
Answer: D