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Question

The difference between a positive proper fraction and its reciprocal is `9/20`. The fraction is :


Options:
A .  `3/5`
B .  `3/10`
C .  `4/5`
D .  `5/4`
Answer: Option C

Let the required fraction be  `x`.  Then , `1/x` - `x` = `9/20`

`therefore`  ` (1-x^2)/(x)`   = `9/20`  `rArr`  20  - `20x^2`  = `9x` `rArr`  `20x^2` + `9x` - 20 = 0

`  rArr`   20`x^2` + 25`x` - 16`x`  - 20 = 0      `rArr`   5`x` (4`x` + 5) - 4(4`x` + 5 )  = 0

`rArr`  (4`x` + 5 ) (5`x` - 4 ) = 0  `rArr` `x` = `4/5`.




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