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DS: Source Princeton Review Practice

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Manager
Joined: 03 Sep 2005
Posts: 135
DS: Source Princeton Review Practice [#permalink]

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14 Sep 2005, 00:05
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I have no clue what this question is asking whatsoever. If you have gone through the princeton review practice tests, maybe you can shed some light?

If 4 d x d 12, is the tens digit of x! prime?

(1) x is even
(2) x! has exactly 3 distinct prime factors
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Life is not measured by the number of breaths you take, but by the number of moments that take your breath away.

Manager
Joined: 06 Aug 2005
Posts: 197

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14 Sep 2005, 01:09
Could you be slightly clearer on the format of the expression please ?

Are there any * or ^ symbols ?
Manager
Joined: 03 Sep 2005
Posts: 135

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14 Sep 2005, 02:11
Richard, that is exactly what I would like to know. I typed it exactly as it appeared in the question.

richardj wrote:
Could you be slightly clearer on the format of the expression please ?

Are there any * or ^ symbols ?

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Life is not measured by the number of breaths you take, but by the number of moments that take your breath away.

Manager
Joined: 06 Aug 2005
Posts: 197

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14 Sep 2005, 03:08
I think there is a typo in the question and d should be < so,

f 4 < x < 12, is the tens digit of x! prime?

(1) x is even
(2) x! has exactly 3 distinct prime factors

[I think we are also supposed to assume x is an integer, because it is not normal to have non-integer factorials, though it can be defined continuous with gamma functions. But way off topic for GMAT.]

Then (1) means x=6, 8, 10
x! = 720, 40320, 3628800
So tens digit x! = 2, 2, 0 (prime, prime, not-prime)
Not sufficient

Then (2)
the first four prime factors are 2,3,5,7
We must have first three, but not fourth.
So x=5 or x=6
x! = 120, 720 (prime, prime)
So sufficient assuming integers

So answer is B assuming integer x.

If not assuming integer X, answer is C, as we would have x=6, x!=720
Senior Manager
Joined: 22 Jun 2005
Posts: 363
Location: London

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14 Sep 2005, 06:40
yes, I think richard got to be right.

i also did a mock test from PR and got the same question.
It must be a typo
Manager
Joined: 03 Sep 2005
Posts: 135

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14 Sep 2005, 13:59
Dang you're good, Richard. B it is!
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Life is not measured by the number of breaths you take, but by the number of moments that take your breath away.

14 Sep 2005, 13:59
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