A batsman makes a score of 100 runs in the 17th inning and thus increases his averages by 5. What is his average after 17th inning? Choose the correct choice from the following answers
A) 39 B) 35 C) 20 D) 40.5 E) 41.5

Rationale: "let the average after 16 th inning = x then total run after 16 th inning = 16 x then total run after 17 th inning = 16 x + 100 then average run after 17 th inning = ( 16 x + 100 ) / 17 ( 16 x + 100 ) / 17 = x + 5 = > 16 x + 100 = 17 x + 85 = > x = 15 x = 15 ; average after 17 th inning = 15 + 5 = 20 answer : c"
Answer: C