BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

pulled out hats

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Newbie | Next Rank: 10 Posts
Posts: 8
Joined: Wed May 27, 2009 11:16 am

pulled out hats

by gmatjem » Sat May 30, 2009 6:20 pm
Please throw your thoughts on this DS :

If a number n is pulled out of a hat at random, what is the probability that 1/2n - 2 ≥ 0?

(1) There are 6 numbers in the hat and each number is an integer.

(2) For every value of n in the hat, 1 ≤ n ≤ 30.
Top
Source: — Data Sufficiency |
Master | Next Rank: 500 Posts
Posts: 119
Joined: Tue Jan 20, 2009 10:16 pm
Thanked: 9 times
GMAT Score:730

by mikeCoolBoy » Sun May 31, 2009 7:02 am
IMO E

My rephrase of the question:

1/2n - 2 ≥ 0 ---> 1/2n >= 2 ---> n >=4. so the question should be

what is the probability that n>=4?

1)

6 numbers in the hat and they are integers
you can construct two sets

s1={1,1,1,1,1,1} the probability of n>=4 is 0
s2={4,4,4,4,4,4} the probability of n>=4 is 1

insufficient

2)

for every value of n in the hat 1<=n<=30

using the same sets we have different values for the probability so statement two is insufficient and combining 1 and 2 as well.
Top
User avatar
Legendary Member
Posts: 682
Joined: Fri Jan 16, 2009 2:40 am
Thanked: 32 times
Followed by:1 members

by Vemuri » Sun May 31, 2009 8:47 am
mikeCoolBoy wrote: My rephrase of the question:

1/2n - 2 &#8805; 0 ---> 1/2n >= 2 ---> n >=4. so the question should be

what is the probability that n>=4?
Are you sure n>=4?

If 1/2n >=2, then 1>=4n ==> n<=1/4
Top
Master | Next Rank: 500 Posts
Posts: 119
Joined: Tue Jan 20, 2009 10:16 pm
Thanked: 9 times
GMAT Score:730

by mikeCoolBoy » Sun May 31, 2009 9:03 am
I assumed that the expression was (1/2)n - 2 >=0.
If the expression is 1/(2n) -2 >=0 then 1/(2n) >=2 --->1/n >= 4

what is the probability that 1/4>= n>0?

1) there are 6 numbers are all are integers
sufficient the probability is 0 because n cannot be <= 1/4 and > 0

2) for every number n in the hat 1<=n<= 30
sufficient the probability is also 0
Top
Post new topic Post Reply
• Page 1 of 1