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If p,s, and t are positive prime numbers, what is the value

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Manager
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If p,s, and t are positive prime numbers, what is the value [#permalink] New post 04 Jun 2008, 12:19
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A
B
C
D
E

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If p,s, and t are positive prime numbers, what is the value of p^3 * s^3 * t^3?
1) p^3 *st=728
2) t=13
Manager
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Re: DS: prime numbers [#permalink] New post 04 Jun 2008, 14:51
Quote:
If p,s, and t are positive prime numbers, what is the value of p^3 * s^3 * t^3?
1) p^3 *st=728
2) t=13

To calculate we need p,q and t
A- Alone not sufficient.
B- Alone not sufficient
But if you combine it togeter
p^3 * s = 728/13=56,

Now, p must be 2, since 1 or 3 wont work. So p=2, t=13 and s=7 Answer = C
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Re: DS: prime numbers [#permalink] New post 04 Jun 2008, 16:51
A

(p^3)*(st) = 728 = 2^3 * 5 * 13

p = 2
s = 5 or 13
t = 13 or 5

but the actual number of s and t does not matter because s^3 * t^3 = (st)^3
so (5*13)^3 is the same as (13*5)^3 = (st)^3 = s^3 * t^3
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Re: DS: prime numbers [#permalink] New post 04 Jun 2008, 17:21
GMAT TIGER wrote:
puma wrote:
If p,s, and t are positive prime numbers, what is the value of p^3 * s^3 * t^3?
1) p^3 *st=728
2) t=13


is there anything missing?

sorry for the confusion:

1) p^3 *st=728
p^3 *st = 2x2x2x7x13

so p = 2, st = 7x13
suff...


2) t=13. nsf

C is a trap. so do not need st. 1 to answer. st 1 is suff....
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Re: DS: prime numbers [#permalink] New post 05 Jun 2008, 00:40
A for me.

Almost went for C

728/8=91 and 91 can be only 13*7 thus A
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Re: DS: prime numbers [#permalink] New post 05 Jun 2008, 05:45
puma wrote:
If p,s, and t are positive prime numbers, what is the value of p^3 * s^3 * t^3?
1) p^3 *st=728
2) t=13



Notice that p^3 *st=728 is an even number.

Also notice that the units digit is 8. This means that p must be 2.

728/8 = 91. s and t are only 2 primes so 91 is divisible by ONly two numbers (other than 1 and itself).

No more work needed here.

2: dsnt help us.


A
Re: DS: prime numbers   [#permalink] 05 Jun 2008, 05:45
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If p,s, and t are positive prime numbers, what is the value

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