og ds 125

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simba12123: Senior | Next Rank: 100 Posts; Posts: 94; Joined: Tue Oct 14, 2008 1:05 pm

og ds 125

by simba12123 » Thu Oct 23, 2008 12:20 pm

if R and S are positive integers, is R/s an integer?

1. every factor os s is also a factor of r

2. every prime factor of s is also a prime factor of r

qa is a

if r ia 4 and s is 2 answer is no. but if r is 2 and s is 4 answer is yes. further, in statement 2 for each prime factor to match; doesnt this mean that the numbers must be the same prime number?

i have qa is b. whats up?!

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Source: Beat The GMAT — Data Sufficiency | Thu Oct 23, 2008 12:20 pm

cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pm; Thanked: 331 times; Followed by:11 members

by cramya » Thu Oct 23, 2008 1:42 pm

if r ia 4 and s is 2 answer is no. but if r is 2 and s is 4 answer is yes. further, in statement 2 for each prime factor to match; doesnt this mean that the numbers must be the same prime number?

I think u reverses what u were trying to say. if r ia 4 and s is 2 answer is yes. but if r is 2 and s is 4 answer is no

Stmt 1) Every factor of s is a factor of r I think this means r is a mutiple of s So r/s will be an integer for sure

SUFF

Stmt 2) Consider 20 and 50 where r=50 s=20

50 = 2*5*5
20 = 2*5*2

Every prime factor of 20 is a prime factor of 50 but 50/20 is not an integer

Consider r=40 s=20,Every prime factor of 20 is also a prime factor 40 and 40/20 is an integer

INSUFF

Hope I am not way off here!

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yezz: Senior | Next Rank: 100 Posts; Posts: 65; Joined: Sun Oct 19, 2008 2:18 pm; Thanked: 1 times

Re: og ds 125

by yezz » Thu Oct 23, 2008 1:47 pm

simba12123 wrote:if R and S are positive integers, is R/s an integer?

1. every factor os s is also a factor of r

2. every prime factor of s is also a prime factor of r

A is NOT suff

in your example

if s = 4 , r = 2 ( every factor of s is not a factor of r ( consider 4)

Last edited by yezz on Thu Oct 23, 2008 1:57 pm, edited 1 time in total.

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pm; Thanked: 331 times; Followed by:11 members

by cramya » Thu Oct 23, 2008 1:48 pm

I looked up the og after I posted and I think og gives a good explanation for statement 2

r=18 s=6 holds good r/s integer
r=18(2*2*3*3) s=8(2*2*2) r/s is not an integer

8's prime factor 2 is in 18 but still 18/8 is not an INTEGER
Hope this helps!

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rohangupta83: Legendary Member; Posts: 541; Joined: Thu May 31, 2007 6:44 pm; Location: UK; Thanked: 21 times; Followed by:3 members; GMAT Score:680

by rohangupta83 » Thu Oct 23, 2008 2:46 pm

(A)

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simba12123: Senior | Next Rank: 100 Posts; Posts: 94; Joined: Tue Oct 14, 2008 1:05 pm

og ds 125

by simba12123 » Fri Oct 24, 2008 6:28 am

this one baffles me. I am not seeing the light on this!

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stop@800: Legendary Member; Posts: 871; Joined: Wed Aug 13, 2008 7:48 am; Thanked: 48 times

Re: og ds 125

by stop@800 » Fri Oct 24, 2008 7:35 am

simba12123 wrote:this one baffles me. I am not seeing the light on this!

Let me try to explain...............
First try to understand the difference between factors and prime factors.

2 2 3 3

Factors of 36 are 1 2 4 3 9 6 12 18 36
Prime factors of 36 are 2 and 3

Now look at the problem
A
every factor os s is also a factor of r

means
R is either equal to or greater than s
and the greater is by an integer mutiple
Ex: r = S = 36
or
r = 72 and s = 36

so we can easily say, even without example, that statement is sufficient.

B
every prime factor of s is a prime factor of r
but we do not know what is the degree, i mean power of that factor in s
it may be possible that power in s is greater and same in R is less.

Example
S = 36, prime factors 2,3
R = 12, prime factors 2,3

also
S = 36, prime factors 2,3
R = 72, prime factors 2,3

so B is insuff

Hope this helps

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