The difference between a positive proper fraction and its reciprocal is 9/20. The fraction is:
Options
A) 4 / 5	B) 5 / 4	C) 3 / 5	D) 2 / 5	E) 3 / 4

Rationale: "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 20 x ^ 2 + 25 x - 16 x - 20 = 0 5 x ( 4 x + 5 ) - 4 ( 4 x + 5 ) = 0 ( 4 x + 5 ) ( 5 x - 4 ) = 0 x = 4 / 5 ( neglecting - ve value ) answer a ) 4 / 5"
Answer: A