Does k have more different prime factors than j?

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Hello,

Can you please tell me how we can solve for C:

If k & j are positive integers, and k is not equal to j, does k have more different prime factors
than j?

(1) k = (10)^j
(2) j = (30)^k

OA: C


I tried to solve as follows:

1) Let j = 1 => k = 10^1 = 10
Here j has no prime factors while k has 2 prime factors i.e. 2 and 5
Hence, answer to our original question is yes

Let j = 30 => k = 10^30
Here j has three prime factors i.e. 2, 3 and 5 while k has 2 prime factors i.e. 2 and 5
Hence, answer to our original question is no

Hence, In-suff.


2) Let k = 1 and j = 30
Here k has no prime factor while j has 3 prime factors i.e. 2, 3 and 5
Here, answer to our original question is no

Let k = 210 and j = 30
Here k has 4 prime factors while j has 3 prime factors
Hence, answer to our original question is yes

Hence, in-suff.


From 1 and 2:

k = 10^j and j = 30^k

I was wondering how we can prove that C is suff. since we now have

k = 10^j = 10^(30^k)

Can you please assist? Thanks a lot.


Best Regards,
Sri
Source: — Data Sufficiency |

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by [email protected] » Tue Apr 01, 2014 11:05 pm
Hi Sri,

Did you transcribe this question correctly. I ask because if you did transcribe it correctly, then this question has a design flaw in it - the math doesn't actually "work"; I'll explain why in a moment.

You've correctly proven that both Facts are INSUFFICIENT on their own, by TESTing VALUES (although there is a typo in your work).

When combining statements, the math won't work because the prompt tells us that K and J are POSITIVE INTEGERS. In Fact 1, K > J; in Fact 2, J > K. In DS questions, the two FACTS will NEVER contradict one another. Whoever wrote this question didn't follow that "design principle"

Whoever wrote this question did try to focus on an algebra "pattern" that shows up on the GMAT and is worth knowing: when you have 2 variables and 2 unique equations, you CAN solve for both variables. When combining those two Facts, you'd have two variables and two unique equations, so you COULD solve it (but you don't have to) and there would be just one answer. That's why the final answer is C.

GMAT assassins aren't born, they're made,
Rich
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by gmattesttaker2 » Sat Apr 12, 2014 12:46 pm
[email protected] wrote:Hi Sri,

Did you transcribe this question correctly. I ask because if you did transcribe it correctly, then this question has a design flaw in it - the math doesn't actually "work"; I'll explain why in a moment.

You've correctly proven that both Facts are INSUFFICIENT on their own, by TESTing VALUES (although there is a typo in your work).

When combining statements, the math won't work because the prompt tells us that K and J are POSITIVE INTEGERS. In Fact 1, K > J; in Fact 2, J > K. In DS questions, the two FACTS will NEVER contradict one another. Whoever wrote this question didn't follow that "design principle"

Whoever wrote this question did try to focus on an algebra "pattern" that shows up on the GMAT and is worth knowing: when you have 2 variables and 2 unique equations, you CAN solve for both variables. When combining those two Facts, you'd have two variables and two unique equations, so you COULD solve it (but you don't have to) and there would be just one answer. That's why the final answer is C.

GMAT assassins aren't born, they're made,
Rich
Hi Rich,

Thanks a lot for the explanation. I tried to plug in some values as follows when combining 1 and 2:

k = (10)^j and j = (30)^k

Let j = 1 => k = 10^1 = 10
j has no prime factors
k has two prime factors i.e. 2 and 5

Since j = 30^k => j = 30^10
j has three prime factors i.e. 2,3 and 5

I was not sure here whether I should take the prime factors for j = 1 or for j = 30^10
Does this have to do with what you have mentioned about this not being an actual GMAT question where-in we wouldn't be running into this kind of situation? Thanks again for your help.

Best Regards,
Sri