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Confused.......

by onedayi'll » Thu Feb 25, 2010 3:52 pm
If N = 1234@ and @ represents the units digit, is a multiple of 5?

@! is not divisible by 5
@ is divisible by 9


I think B is correct, but looks like i'm wrong.
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by hrishi19884 » Fri Feb 26, 2010 12:29 am
1) @! - > does not indicate anything about what @ could be (it could be anything) ---ruled out

2) @ is div by 9 , so @ can be 9 or 0

If @ is 9 then number is not div by 5

If @ is 0, then number is div by 5

Hence the ans should be E
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by ajith » Fri Feb 26, 2010 12:37 am
onedayi'll wrote:If N = 1234@ and @ represents the units digit, is a multiple of 5?

@! is not divisible by 5
@ is divisible by 9


I think B is correct, but looks like i'm wrong.

1) is not sufficient (0! =1 is not divisible by 5 and 5! is divisible)

2) @ is divisible by 9; @ can be 0 or 9 - Insufficient

Combining, only 0 remains hence the number is divisible by 5 Hence, C
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by hrishi19884 » Fri Feb 26, 2010 1:30 am
ajith wrote:
1) is not sufficient (0! =1 is not divisible by 5 and 5! is divisible)
It is given that @! is div by 5 so it can be any number 12, 13, 66, 72
only thing that ! should not be 5 or 0 but @ can be anything (0,5,4,6,3) as "@!" rep "26" or "76"...etc

Your judgment would have been right if it was "!@" and not "@!"

So we cannot say that @ cant be 0 or 5 but we can say that "!"(unit digit) cant be 0 or 5

quest doesn't mentions anything about "!"

hence we cannot combine to get "0" . Hence I think E
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by ajith » Fri Feb 26, 2010 1:35 am
hrishi19884 wrote:
It is given that @! is div by 5 so it can be any number 12, 13, 66, 72
only thing that ! should not be 5 or 0 but @ can be anything (0,5,4,6,3) as "@!" rep "26" or "76"...etc

Your judgment would have been right if it was "!@" and not "@!"

So we cannot say that @ cant be 0 or 5 but we can say that "!"(unit digit) cant be 0 or 5

quest doesn't mentions anything about "!"

hence we cannot combine to get "0" . Hence I think E
Hang on my friend,

'!' is the factorial operation unless otherwise mentioned

0! = 0; 1! = 1 , 2! =2 , 3! =6, 4! =24 etc etc ..........

Now recalculate and tell me whether we concur
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by hrishi19884 » Fri Feb 26, 2010 1:44 am
lol....you ribbed that out ........I totally forgot its a factorial not a digit......thanks.

Now since its a factorial, yes C is the one.

as 0! = 1 and 1 is not div by 5.

Thanks brother!

Do you think such questions appear in real GMAT?
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by ajith » Fri Feb 26, 2010 1:46 am
hrishi19884 wrote:lol....you ribbed that out ........I totally forgot its a factorial not a digit......thanks.

Now since its a factorial, yes C is the one.

as 0! = 1 and 1 is not div by 5.

Thanks brother!

Do you think such questions appear in real GMAT?
Concept wise, it is totally within the scope

With respect to ambiguity, I am none to comment, may be experts can!
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by Ian Stewart » Fri Feb 26, 2010 11:17 am
ajith wrote:
0! = 0; 1! = 1 , 2! =2 , 3! =6, 4! =24 etc etc ..........

Now recalculate and tell me whether we concur
There's one small typo in the above; it should say 0! = 1.

That said, I have never seen an official GMAT question where you need to know what 0! means. I have only seen questions involving factorials of *positive* integers. I have seen some prep company questions that test whether you know the meaning of 0!; these aren't likely to be at all helpful to study.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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