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Joined: 07 Dec 2014
Posts: 1224
xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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Difficulty:   35% (medium)

Question Stats: 69% (02:07) correct 31% (02:22) wrong based on 51 sessions

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xy and yx are reversed two digit integers. If the sum of the digits equals the difference between the squares of the digits, what could be the product of the digits?

A. 8
B. 12
C. 15
D.18
E. 24
Intern  B
Joined: 02 May 2018
Posts: 1
Re: xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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Just calculate each option. For B 1+2=3 and 2^2-1=4-1=3.

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Manager  S
Joined: 11 Apr 2018
Posts: 125
Location: India
GPA: 4
WE: Information Technology (Computer Software)
Re: xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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1
If the sum of the digits equals the difference between the squares of the digits.
=> (x + y) = (x^2 - y^2)
=> (x + y) = (x + y)(x - y)
=>x-y = 1
So, XY = 21, 32, 43, 54, 65, 76, 87, 98

From the above possible numbers, the only product in options is 12 for number 43.

Manager  B
Joined: 01 Jan 2019
Posts: 67
Concentration: Finance, Economics
GPA: 3.24
Re: xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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Lowkya wrote:
If the sum of the digits equals the difference between the squares of the digits.
=> (x + y) = (x^2 - y^2)
=> (x + y) = (x + y)(x - y)
=>x-y = 1
So, XY = 21, 32, 43, 54, 65, 76, 87, 98

From the above possible numbers, the only product in options is 12 for number 43.

Can u explain how did u arrive at B? It is asking product of the digits

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Manager  S
Joined: 11 Apr 2018
Posts: 125
Location: India
GPA: 4
WE: Information Technology (Computer Software)
Re: xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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1
Shef08 wrote:
Lowkya wrote:
If the sum of the digits equals the difference between the squares of the digits.
=> (x + y) = (x^2 - y^2)
=> (x + y) = (x + y)(x - y)
=>x-y = 1
So, XY = 21, 32, 43, 54, 65, 76, 87, 98

From the above possible numbers, the only product in options is 12 for number 43.

Can u explain how did u arrive at B? It is asking product of the digits

Posted from my mobile device

Sure.
Yes, it is asking for the product of digits.

From the above solution you can see that possible numbers are XY = 21, 32, 43, 54, 65, 76, 87, 98.
=> Possible products are - 2, 6, 12,20, 30, 42, 56, 72.

Only 12 is in the options. So, B.

Hope this helps.

Thanks
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Re: xy and yx are reversed two digit integers. If the sum of the digits eq  [#permalink]

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gracie wrote:
xy and yx are reversed two digit integers. If the sum of the digits equals the difference between the squares of the digits, what could be the product of the digits?

A. 8
B. 12
C. 15
D.18
E. 24

Without loss of generality of the problem, we can assume that x > y. So we have:

x + y = x^2 - y^2

x + y = (x + y)(x - y)

Dividing both sides of the equation by (x + y) (since it won’t be 0), we have:

1 = x - y

The only way we can get (x - y) to equal 1 is if x is one more than y. Therefore, we see that x and y must be consecutive integers. Of the answer choices, we see that only 12 can be the product of two consecutive integers (12 = 3 x 4), so 12 is the correct answer.

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If you find one of my posts helpful, please take a moment to click on the "Kudos" button. Re: xy and yx are reversed two digit integers. If the sum of the digits eq   [#permalink] 03 Apr 2019, 18:28
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