What is y in terms of x ?

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uptowngirl92: Master | Next Rank: 500 Posts; Posts: 447; Joined: Sun Apr 19, 2009 9:08 pm; Location: Kolkata,India; Thanked: 7 times; GMAT Score:670

by uptowngirl92 » Tue Jun 09, 2009 7:45 pm

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

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Source: Beat The GMAT — Problem Solving | Tue Jun 09, 2009 7:45 pm

ssmiles08: Master | Next Rank: 500 Posts; Posts: 472; Joined: Sun Mar 29, 2009 6:54 pm; Thanked: 56 times

by ssmiles08 » Tue Jun 09, 2009 8:17 pm

IMO E

n = xy (where x and y are two different digits)

it can also be written as 10x+y = n

reverse of n = 10y + x

the question stem deduced is: 10y + x = 10x + y + 9

9y - 9x = 9

y - x = 1

y = 1 + x

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abhinav85: Master | Next Rank: 500 Posts; Posts: 179; Joined: Mon Dec 29, 2008 4:41 am; Thanked: 2 times

by abhinav85 » Fri Jun 12, 2009 7:28 am

I Think IMO is B.

becoz if you go by the ques it says that

tens digit x and the units digit y that means 10x + y
and when we reverse this we get 10y + x + 9

futher simplify it we get

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

y = 9 - x.

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truplayer256: Master | Next Rank: 500 Posts; Posts: 392; Joined: Thu Jan 15, 2009 12:52 pm; Location: New Jersey; Thanked: 76 times

by truplayer256 » Fri Jun 12, 2009 11:02 am

I Think IMO is B.

becoz if you go by the ques it says that

tens digit x and the units digit y that means 10x + y
and when we reverse this we get 10y + x + 9

futher simplify it we get

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

y = 9 - x.

How is x=y+9 equal to y=9-x? It should really be equal to y=x-9 and that's not even an answer choice. The mistake that you made is that you added the 9 to the number whose digits were reversed instead of adding the 9 to the original integer n. I guess you were confused with the wording.

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ssmiles08: Master | Next Rank: 500 Posts; Posts: 472; Joined: Sun Mar 29, 2009 6:54 pm; Thanked: 56 times

by ssmiles08 » Fri Jun 12, 2009 12:44 pm

abhinav85 wrote:I Think IMO is B.

becoz if you go by the ques it says that

tens digit x and the units digit y that means 10x + y
and when we reverse this we get 10y + x + 9

futher simplify it we get

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

y = 9 - x.

Hey abhinav85,

What you did was n = reverse + 9

The question stem is saying that (reverse of N) = N + 9

So it is (10y + x) = (10x + y) + 9

Also when you are dividing by 9, you need to divide everything by 9, not just x and y.

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mehravikas: Legendary Member; Posts: 1161; Joined: Mon May 12, 2008 2:52 amFollowed by: 1 member; Location: Sydney; Thanked: 23 times

by mehravikas » Thu Jun 25, 2009 6:51 pm

IMO - E

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