It is currently 19 Oct 2017, 04:07

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

m15 10

Author Message
Director
Joined: 01 Apr 2008
Posts: 875

Kudos [?]: 843 [0], given: 18

Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014

Show Tags

19 Sep 2009, 04:04
Set $$S$$ consists of all prime integers less than 10. If two numbers are chosen form set $$S$$ at random, what is the probability that the product of these numbers will be greater than the product of the numbers which were not chosen?

I think it should be specified that two 'different' numbers are chosen. if not then 7,7 is also a possibility and then the probability will not be 1/2.

Kudos [?]: 843 [0], given: 18

Manager
Joined: 10 Jul 2009
Posts: 164

Kudos [?]: 117 [0], given: 8

Show Tags

19 Sep 2009, 12:54
S = { 2,3,5,7}
Number of ways for chosing two numbers = 4c2 = 6
Number of out comes where product of two numbers is greater than product of remaining numbers = 3 (3*7, 5*7, 3*5)

So probability = 3/6 = 1/2

Different numbers need not be specified as the set has each number only one. If it is repeated many times then "different number" wording should be used.

Kudos [?]: 117 [0], given: 8

Intern
Joined: 23 Sep 2009
Posts: 12

Kudos [?]: [0], given: 0

Show Tags

24 Sep 2009, 01:15
Set of prime numbers less than 10 is S = {2, 3, 5, 7}

Using counting methods, the number of ways to choose 2 items out of 4 is 4!/2!*2! = 6

The 6 possible products are:
2 x 3 = 6
2 x 5 = 10
2 x 7 = 14
3 x 5 = 15
3 x 7 = 21
5 x 7 = 35

... of which the last 3 products are larger than the first 3 products.

Therefore, the probability of selecting 2 numbers with a product that is larger than those not selected is 3/6 = 0.5

Kudos [?]: [0], given: 0

Re: m15 10   [#permalink] 24 Sep 2009, 01:15
Display posts from previous: Sort by

m15 10

Moderator: Bunuel

 Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.