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If r and s are positive integers, is r/s an integer?

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If r and s are positive integers, is r/s an integer? [#permalink] New post 23 Feb 2012, 07:13
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If r and s are positive integers, is r/s an integer?

(1) Every factor of s is also a factor of r.
(2) Every prime factor of s is also a prime factor of r.
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 23 Feb 2012, 07:26
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If r and s are positive integers, is r/s an integer?

(1) Every factor of s is also a factor of r. If every factor of s is also factor of r, then in fraction r/s, s will just be reduced and we get an integer. Sufficient.

(2) Every prime factor of s is also a prime factor of r. The powers of prime factors of s could be higher than powers of prime factors of r. eg 25/125=1/5 not an integer. Not sufficient.

Answer: A.

Hope it's clear.
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is x/y is an integer [#permalink] New post 11 Apr 2012, 12:05
All
could you provide ur thoughts on this please?


if x and y are positive integers, is x/y is an integer?

(1) every prime factor of x is also the prime factor of y
(2) every factor of x is also a factor of y

i went with D, since the word "every" confused me
but seems missed something
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Re: is x/y is an integer [#permalink] New post 11 Apr 2012, 12:11
Galiya wrote:
All
could you provide ur thoughts on this please?


if x and y are positive integers, is x/y is an integer?

(1) every prime factor of x is also the prime factor of y
(2) every factor of x is also a factor of y

i went with D, but seems missed something


The answer is B because:

if every prime factor x is also a prime factor of y - lets take an example:

X= 30 prime factors = 2, 3, 5
y = 60 prime factors = 2, 3, 5

but x/y = 1/2

whereas if all factors of x = all factors of y that simply tells us that x is y inclusive and therefore totally divisible by y.
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Re: is x/y is an integer [#permalink] New post 11 Apr 2012, 12:17
Expert's post
Galiya wrote:
All
could you provide ur thoughts on this please?


if x and y are positive integers, is x/y is an integer?

(1) every prime factor of x is also the prime factor of y
(2) every factor of x is also a factor of y


i went with D, since the word "every" confused me
but seems missed something


Proper version of this question is in the initial post.
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 11 Apr 2012, 12:25
Bunuel
what about the word "every" - according to this i picked up numbers which satisfied this condition.
And one more point-official explanation "takes" the numbers 18 and 8, to explain the answer.
But 18 has the prime factors 2 and 3, but 8 hasn't 3 as a prime factor - what means not every factor of x is also a prime factor of y - and this contradicts with the statement
I just need to clarify -to avoid such a confusion on the exam
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 11 Apr 2012, 12:28
Expert's post
Galiya wrote:
Bunuel
what about the word "every" - according to this i picked up numbers which satisfied this condition.
And one more point-official explanation "takes" the numbers 18 and 8, to explain the answer.
But 18 has the prime factors 2 and 3, but 8 hasn't 3 as a prime factor - what means not every factor of x is also a prime factor of y - and this contradicts with the statement
I just need to clarify -to avoid such a confusion on the exam


Let's refer to the question in the initial post: which statement are you talking about?
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 11 Apr 2012, 12:30
i mean this one
(2) Every prime factor of s is also a prime factor of r.
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 11 Apr 2012, 12:40
Expert's post
Galiya wrote:
i mean this one
(2) Every prime factor of s is also a prime factor of r.


There is an example given in my post which satisfies the given condition and doesn't give an integer value of r/s.

(2) Every prime factor of s is also a prime factor of r. The powers of prime factors of s could be higher than powers of prime factors of r.

For example: if s=5^3 and r=5^2 then every prime of 125 (in fact its only prime 5) IS also a prime of 25 but r/s=25/125 is not an integer.
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 23 Aug 2012, 20:14
What if S>R? It doesn't say that R>S. It just says they are positive integers.

For first statement:
R>S = 20/10 = 2 --> Integer
S>R = 10/20 = .5 --> Not an integer

For the second statement:
R>S = 50/5 = 10 --> Integer
S>R = 5/50 = .5 --> Not an integer

That is why I picked E. Can you please explain why my reasoning is incorrect? Thanks!
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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 24 Aug 2012, 01:04
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KAS1 wrote:
What if S>R? It doesn't say that R>S. It just says they are positive integers.

For first statement:
R>S = 20/10 = 2 --> Integer
S>R = 10/20 = .5 --> Not an integer

For the second statement:
R>S = 50/5 = 10 --> Integer
S>R = 5/50 = .5 --> Not an integer

That is why I picked E. Can you please explain why my reasoning is incorrect? Thanks!


For the first statement s cannot be greater than r. If every factor of s is also factor of r, then r\geq{s}. Your example, (r=10 and s=20), is not possible, because 4 is a factor of s but not a factor of r.

Hope it's clear.
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Re: If a and b are positive integers, is ‘a’ a multiple of b? [#permalink] New post 25 Sep 2012, 10:24
ankit0411 wrote:
If a and b are positive integers, is ‘a’ a multiple of b?

(1) Every prime factor of b is also a prime factor of a (2) Every factor of b is also a factor of a



(1) Consider for example a = 2\cdot3=6 and b = 2^2\cdot3=12, so obviously a is not a multiple of b.
If a = 12 and b = 6, then of course a is a multiple of b.
Not sufficient.

(2) b is a factor of itself, so it is also a factor of a, which means that a is a multiple of b.
Sufficient.

Answer B.
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DS : X and Y are two positive integers [#permalink] New post 24 Oct 2012, 22:25
Hi,

I'm trying to figure out this one.

X and Y are two positive integers. Is x divided by y an integer?

(1) All of Y's factors are also factors of X.

(2) Each prime factor of Y is also a prime factor of X.

Any pointers, please?

A, B, C, D or E?

Thanks.
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Re: DS : X and Y are two positive integers [#permalink] New post 24 Oct 2012, 22:33
elegan wrote:
Hi,

I'm trying to figure out this one.

X and Y are two positive integers. Is x divided by y an integer?

(1) All of Y's factors are also factors of X.

(2) Each prime factor of Y is also a prime factor of X.

Any pointers, please?

A, B, C, D or E?

Thanks.


1) Y itself is a factor of Y. Hence Y is also a factor of X. Sufficient

2)Suppose X = 2 and Y = 8. Answer is No. If Y = 2 and X =8 answer is yes. Insufficient

Answer is A.

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Re: If r and s are positive integers, is r/s an integer? [#permalink] New post 12 Jan 2014, 05:35
BANON wrote:
If r and s are positive integers, is r/s an integer?

(1) Every factor of s is also a factor of r.
(2) Every prime factor of s is also a prime factor of r.



Basically, the question asks us if s is a factor of r.


1) This is significant, because we are told something about every factor of s. Let's say the products of the factors of s = n, then 1) gives us n*r.. is n*r/n an integer? Of course.. So 1) is sufficient

2) This only tells us a fraction of the information that 1) tells us, since 2) restricts the factors to primes.. But we don't know if s has other factors that are NOT shared by r, and thus 2) is insufficient..


So A is correct
Re: If r and s are positive integers, is r/s an integer?   [#permalink] 12 Jan 2014, 05:35
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