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500 ps test23 #15

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dunkin77 Really wants to Beat The GMAT! Default Avatar
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500 ps test23 #15 Post Mon Apr 16, 2007 12:02 pm
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  • Lap #[LAPCOUNT] ([LAPTIME])
    15. 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


    Hi,

    I though the answer is D) but turned out to be E). Can anyone explain why??

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    jayhawk2001 Community Manager
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    Post Mon Apr 16, 2007 9:02 pm
    dunkin77 wrote:
    15. 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


    Hi,

    I though the answer is D) but turned out to be E). Can anyone explain why??
    n can be written as 10x + y

    If we reverse x and y, we get a number of the form 10y + x

    10y + x = 9 + 10x + y
    9y = 9x + 9
    y = x + 1

    Cybermusings GMAT Destroyer! Default Avatar
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    Post Tue Apr 17, 2007 3:25 am
    Original number - 10x+y
    New number - 10y+x
    10y+x-10x-y=9
    9y-9x=9
    Y-x=1
    y=x+1

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