Aptitude - Numbers - Discussion
Discussion Forum : Numbers - General Questions (Q.No. 26)
26.
The difference between a positive proper fraction and its reciprocal is 9/20. The fraction is:
Answer: Option
Explanation:
| Let the required fraction be x. Then | 1 | - x = | 9 |
| x | 20 |
 |
1 - x2 | = | 9 |
| x | 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
| x = | 4 |
| 5 |
Discussion:
53 comments Page 5 of 6.
Krishna Sowjanya said:
6 years ago
Let the proper fraction be x/y.
Then (x/y)-(y/x) = 9/20.
LCM of x and y = xy.
Therefore the denominator xy =20 obviously.
So, by cross-checking the options in option C we have 4 * 5=20. i.e., x=4 and y=5.
Then (x/y)-(y/x) = 9/20.
LCM of x and y = xy.
Therefore the denominator xy =20 obviously.
So, by cross-checking the options in option C we have 4 * 5=20. i.e., x=4 and y=5.
(1)
Jyothi said:
6 years ago
Thank You @Akash.
Stephen said:
6 years ago
If the fraction is 4/5.
Then 4/5(fraction)-5/4(reciprocal) = -9/20.
So, I believed the answer(fraction) = 5/4.
Then 4/5(fraction)-5/4(reciprocal) = -9/20.
So, I believed the answer(fraction) = 5/4.
Nisha said:
6 years ago
Hello everyone,
I hope this may help you.
Keeping all these X things aside, there is a simpler way.
Fraction means 4/5 and it's reciprocal is simply upside-down. That means 5/4. So here the difference is already given. So for each option, we just need to subtract the reciprocal of the same fraction.
So, 4/5-5/4 = 9/20.
As simple as that.
Thank you!
I hope this may help you.
Keeping all these X things aside, there is a simpler way.
Fraction means 4/5 and it's reciprocal is simply upside-down. That means 5/4. So here the difference is already given. So for each option, we just need to subtract the reciprocal of the same fraction.
So, 4/5-5/4 = 9/20.
As simple as that.
Thank you!
(4)
Saran Satz said:
5 years ago
As per the question, y/x - x/y = 9/20,
(y2-x2) / xy = 9/20.
So, we can just take xy=20,
now check options, substitute the values of x & y.
option a) 3*5=15 (not equal to 20),
b) 3*10=30 (not equal to 20),
c) 4*5= 20 (bingo),
d) 4*3=12 (not equal to 20),
So, the answer is option C.
(y2-x2) / xy = 9/20.
So, we can just take xy=20,
now check options, substitute the values of x & y.
option a) 3*5=15 (not equal to 20),
b) 3*10=30 (not equal to 20),
c) 4*5= 20 (bingo),
d) 4*3=12 (not equal to 20),
So, the answer is option C.
(8)
Gayathri said:
5 years ago
Simple Logic.
Give answer is 9/20 (If we do a difference for proper fraction and it's reciprocal).
We take LCM while calculating the difference between fractions and given answer is 9/20 and got LCM as "20".
So, check options which get LCM as 20.
And option 4/5 gives LCM 20 and that's it!
Give answer is 9/20 (If we do a difference for proper fraction and it's reciprocal).
We take LCM while calculating the difference between fractions and given answer is 9/20 and got LCM as "20".
So, check options which get LCM as 20.
And option 4/5 gives LCM 20 and that's it!
(3)
Karthik said:
5 years ago
Please anyone explain me in detail.
Shanu said:
5 years ago
Why 1-x^2/x? Please explain it.
(1)
Shama M said:
4 years ago
Since they have mentioned proper fraction (which is always less than 1), we assumed the difference to be 1/x - x.
(2)
Ashutosh rusiya said:
4 years ago
Take x is a fraction number and 1/x would be its reciprocal number and x-1/x =9/20.
(2)
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