The difference between a positive proper fraction and its reciprocal is 9 / 20. Then the fraction is :
Choose the correct choice from the following answers.
A) 4 / 0	B) 4 / 1	C) 4 / 5	D) 4 / 2	E) 4 / 3

Rationale: "explanation : let the required fraction be x . then , ( 1 / x ) - x = 9 / 20 1 - x ^ ( 2 ) / x = 9 / 20 = > 20 - 20 * x ^ ( 2 ) = 9 * x . 20 * x ^ ( 2 ) + 9 * x - 20 = 0 . = > ( 4 * x + 5 ) ( 5 * x - 4 ) = 0 . = > x = 4 / 5 . answer : c ) 4 / 5"
Answer: C