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Source: — Data Sufficiency |
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by sam2304 » Thu Jan 12, 2012 5:48 am
sud21 wrote:What is the unit's digit of X?
1). x/(10^n)=25^2
2). n^2=1
X = 25^2 * 10^n
10 raised to the power of n will have its units digit as 0. Hence X's unit digit is 0.

SUFF.

With B, we don't have the relation between n and x, so INSUFF

IMO A.
Last edited by sam2304 on Thu Jan 12, 2012 6:22 am, edited 1 time in total.
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by user123321 » Thu Jan 12, 2012 6:06 am
1) we cannot determine units digit because we dont know the value of n. hence insuff.
2) n can be 1 or -1. x has no bearing so insuff.

using both still we dont know since unit's digit can be 0 or 2. hence insuff.

[spoiler]imo E?[/spoiler]

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by ArunangsuSahu » Thu Jan 12, 2012 7:40 am
TRICK:

Statement 1:

x=62.5,n=-1,x/n=625
x=6250,n=1,x/n=625

INSUFFICIENT

Statement 2:
n=-1 or +1

INSUFFICIENT


Combining(1) and (2) also Insufficient

(E) is the choice
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by mankey » Thu Jan 12, 2012 10:09 am
Also nowhere it is mentioned that n is an Integer. n can take any value, even a fraction, unless explicitly mentioned that it cant.

Am I right in my observation. Some expert please clarify.

Thanks.
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by sud21 » Fri Jan 13, 2012 12:01 pm
mankey wrote:Also nowhere it is mentioned that n is an Integer. n can take any value, even a fraction, unless explicitly mentioned that it cant.

Am I right in my observation. Some expert please clarify.

Thanks.
If n is an integer then still the answer will be E.

St.1 x/(10^n)=25^2

n can be any integer from 0 to 9

St.1 x/(10^n)=25^2 , x=25^2*10^n

10 raised to the power of n which is 0 will have its units digit as 5 because 10^0=1 and 25^2=625 and 625*1=625.

But if n is any integer from 1 to 9 then 10 raised to the power of n will have its units digit as 0. Insufficient.

St.2 n^2=1 , nothing about x. Insufficient.

Taking both, n can be +1 or -1.

if n=1 then units digit is 0 but if n=-1 then 25^2/10=62.5, then units digit is 2. Insufficient.

Ans. E
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