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500 ps test23 #15

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by dunkin77 » Mon Apr 16, 2007 11:02 am
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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Re: 500 ps test23 #15

by jayhawk2001 » Mon Apr 16, 2007 8:02 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
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by Cybermusings » Tue Apr 17, 2007 2:25 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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