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If the tens digit x and the units digit y of a positive

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If the tens digit x and the units digit y of a positive [#permalink]  07 Mar 2012, 15:32
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67% (02:10) correct 32% (00:50) wrong based on 1 sessions
If the tens digit x and the units digit y of a positive integer n are reversed, the resulting integer is 9 more than n. What is y in terms of x?

A. 10 - x
B. 9 - x
C. x + 9
D. x - 1
E. x + 1
[Reveal] Spoiler: OA

Last edited by Bunuel on 07 Mar 2012, 15:40, edited 1 time in total.
Edited the OA
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Re: PT #11 PS 3 Q 15 [#permalink]  07 Mar 2012, 15:39
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eybrj2 wrote:
If the tens digit x and the units digit y of a positive integer n are reversed, the resulting integer is 9 more than n. What is y in terms of x?

A. 10 - x
B. 9 - x
C. x + 9
D. x - 1
E. x + 1

n=10x+y and n'=10y+x --> n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

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Re: If the tens digit x and the units digit y of a positive [#permalink]  07 Mar 2012, 22:07
I plugged in with the numbers 23 and 32.

x=2, y=3 therefore y must be x+1.
____
Bunuel,

I followed your solution up until the last portion. Could you explain how you solved the equation into y=x+1? Thanks.
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Re: If the tens digit x and the units digit y of a positive [#permalink]  07 Mar 2012, 22:48
damham17 wrote:
I plugged in with the numbers 23 and 32.

x=2, y=3 therefore y must be x+1.
____
Bunuel,

I followed your solution up until the last portion. Could you explain how you solved the equation into y=x+1? Thanks.

Welcome to GMAT Club.

First of all let me say that plug-in method is fine for this question and your approach is correct.

As for my solution: n'-n=(10y+x)-(10x+y)=9 --> 9y-9x=9 --> y-x=1 --> y=x+1.

Hope it's clear.
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Re: PT #11 PS 3 Q 15 [#permalink]  20 Jun 2012, 03:29
Bunuel wrote:
eybrj2 wrote:
If the tens digit x and the units digit y of a positive integer n are reversed, the resulting integer is 9 more than n. What is y in terms of x?

A. 10 - x
B. 9 - x
C. x + 9
D. x - 1
E. x + 1

n=10x+y and n'=10y+x --> n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

Can anybody clear this for me

suppose I take first number as 10y + x and reverse it to get 10x + y

Then according to the equation (10x + y) - (10y + x ) = 9
9x -9y= 9
x-y=1
y= x-1

so why are we getting two different answers.

if I take first number to be 10x + y and reverse it to get 10y +x
then (10y + x) - (10x +y)= 9y- 9x=9
y-x=1
y= x+1

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Re: PT #11 PS 3 Q 15 [#permalink]  20 Jun 2012, 03:37
stne wrote:
Bunuel wrote:
eybrj2 wrote:
If the tens digit x and the units digit y of a positive integer n are reversed, the resulting integer is 9 more than n. What is y in terms of x?

A. 10 - x
B. 9 - x
C. x + 9
D. x - 1
E. x + 1

n=10x+y and n'=10y+x --> n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

Can anybody clear this for me

suppose I take first number as 10y + x and reverse it to get 10x + y

Then according to the equation (10x + y) - (10y + x ) = 9
9x -9y= 9
x-y=1
y= x-1

so why are we getting two different answers.

if I take first number to be 10x + y and reverse it to get 10y +x
then (10y + x) - (10x +y)= 9y- 9x=9
y-x=1
y= x+1

You cannot arbitrary assign which will be the "first" number and which will be the "second", since the stem explicitly clears that.

Positive integer n has the tens digit x and the units digit y, so n=10x+y;

Reversed integer, say n', has the tens digit y and the units digit x, so n'=10y+x;

We are also told that " the resulting integer (so n') is 9 more than n", which means n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

Hope it's clear.
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Re: PT #11 PS 3 Q 15 [#permalink]  20 Jun 2012, 03:44
Bunuel wrote:
stne wrote:
Bunuel wrote:
If the tens digit x and the units digit y of a positive integer n are reversed, the resulting integer is 9 more than n. What is y in terms of x?

A. 10 - x
B. 9 - x
C. x + 9
D. x - 1
E. x + 1

n=10x+y and n'=10y+x --> n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

Can anybody clear this for me

suppose I take first number as 10y + x and reverse it to get 10x + y

Then according to the equation (10x + y) - (10y + x ) = 9
9x -9y= 9
x-y=1
y= x-1

so why are we getting two different answers.

if I take first number to be 10x + y and reverse it to get 10y +x
then (10y + x) - (10x +y)= 9y- 9x=9
y-x=1
y= x+1

You cannot arbitrary assign which will be the "first" number and which will be the "second", since the stem explicitly clears that.

Positive integer n has the tens digit x and the units digit y, so n=10x+y;

Reversed integer, say n', has the tens digit y and the units digit x, so n'=10y+x;

We are also told that " the resulting integer (so n') is 9 more than n", which means n'-n=(10y+x)-(10x+y)=9 --> y=x+1.

Hope it's clear.

Its clear now , great. Thank you
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Re: PT #11 PS 3 Q 15   [#permalink] 20 Jun 2012, 03:44
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