Correct Answer: Option C
Let the required fraction be x.
Then (1/x) - x = 9/20
So, (1 - x2)/x = 9/20
=> 20 - 20x2 = 9x
=> 20x2 + 9x - 20 = 0
=> 20x2 + 25x - 16x - 20 = 0
=> 5x(4x + 5) - 4(4x + 5) = 0
=> (4x + 5)(5x - 4) = 0
So, x = 4/5
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