An idea to solve this DS question??

Question

For statement one, two numbers 3 and 31 are YES. but, when I started checking for all the prime numbers, 3,5,7,11,13..... I ended up thinking it satisfies only for 3 after checking till 17. there is clearly no pattern

it was a silly mistake, but because of time constraints we might not check till 31. so, is there any other trick to solve for statement ?? __ gmat in 10 days!

akshayk · Answer

S1 -> 2(x+1) is a cube of a positive integer so the quickest thing to do it start checking for positive even cubes, as 2(x+1) cannot be odd. So x = 3, 31,... Insufficient.

2^3 = 8 => x = 3
4^3 = 64 => x = 31

Sent from my iPhone using GMAT Club Forum

broall · Answer

Check here https://gmatclub.com/forum/if-x-is-a-pr ... 88363.html

EMPOWERgmatRichC · Answer

Hi Viserion99,

To start, you should really post these 'subject-specific' questions in the proper forums. The DS forum can be found here:

https://gmatclub.com/forum/gmat-data-su ... cy-ds-141/

To answer your question though, you have to consider which 'part' of the prompt to focus on first. You chose to focus on the "prime" and try to find the 'cube'... but what if you had focused on the 'cube' and "worked backwards" to see if there was a prime involved.

For example, we know that (2X+2) is the cube of a POSITIVE INTEGER... so that cube COULD be...
1^3 = 1
2^3 = 8
3^3 = 27
4^3 = 64

With just these four examples, you can find three different primes (X=3, X=17 and X=31).

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

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An idea to solve this DS question??

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