A waiter's salary consists of his salary and tips. During one week his tips were 5/4 of his salary. What fraction of his income came from tips ?  Choose the correct choice from the following.
A) 4 / 9 B) 5 / 4 C) 5 / 8 D) 5 / 9 E) 6 / 9

Rationale: "income = salary ( s ) + tips = s + s * 5 / 4 = s * 9 / 4 tips = s * 5 / 4 fraction of his income came from tips = ( s * 5 / 4 ) / ( s * 9 / 4 ) = 5 / 9 answer : d"
Answer: D