It is currently 17 Oct 2017, 15:37

### 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

# The purpose of this problem is to exploit a weakness used by

Author Message
TAGS:

### Hide Tags

Current Student
Joined: 29 Jan 2005
Posts: 5207

Kudos [?]: 434 [1], given: 0

The purpose of this problem is to exploit a weakness used by [#permalink]

### Show Tags

17 Nov 2005, 23:11
1
KUDOS
The purpose of this problem is to exploit a weakness used by ETS: complimentary answer choices. Almost always in complimentary probability questions, there are a pair of "LUCKY TWINS" among the answer choices. If in doubt and pressed for time, choose a TWIN by logical deduction.

Let`s take a crack at this Project GMAT bad boy without making lengthy calculations. Duttist, GSR, Titleist, Laxie, Gamjatang, Wilfred, Nakib, etc... NO PENCILS allowed! Please break out the big guns and explain your deductive thought process.

#50: Set S consists of numbers 2, 3, 6, 48, and 164. Number K is computed by multiplying one random number from set S by one of the first 10 non-negative integers, also selected at random. If Z=6^K, what is the probability that 678,463 is not a multiple of Z?

a. 10%
b. 25%
c. 50%
d. 90%
e. 100%

*LUCKY TWINS

Kudos [?]: 434 [1], given: 0

Director
Joined: 21 Aug 2005
Posts: 786

Kudos [?]: 28 [0], given: 0

### Show Tags

17 Nov 2005, 23:22
Well, my probability skills is not one that i can boast of
Looking at this, the number 678,463 seems to be a prime number (atleast not divisible by (2, 3, 4, 6, 7, 8, 9, 11...).
Also, 6^k is even.
On the exam I will go for E) 100%

Kudos [?]: 28 [0], given: 0

GMAT Club Legend
Joined: 07 Jul 2004
Posts: 5036

Kudos [?]: 436 [0], given: 0

Location: Singapore

### Show Tags

17 Nov 2005, 23:27
Could you elaborate a little more on your lucky twins and how you came to choose 10% and 90% as your twins?

Kudos [?]: 436 [0], given: 0

Current Student
Joined: 29 Jan 2005
Posts: 5207

Kudos [?]: 434 [0], given: 0

### Show Tags

17 Nov 2005, 23:34
ywilfred wrote:
Could you elaborate a little more on your lucky twins and how you came to choose 10% and 90% as your twins?

.9+.1=1 (I like your humor Wilfred)

Kudos [?]: 434 [0], given: 0

Current Student
Joined: 29 Jan 2005
Posts: 5207

Kudos [?]: 434 [0], given: 0

### Show Tags

17 Nov 2005, 23:38
gsr wrote:
Well, my probability skills is not one that i can boast of
Looking at this, the number 678,463 seems to be a prime number (atleast not divisible by (2, 3, 4, 6, 7, 8, 9, 11...).
Also, 6^k is even.
On the exam I will go for E) 100%

E is not a LUCKY TWIN (no corresponding 0% among the answer choices) so no "Yukay" for you GSR.

Kudos [?]: 434 [0], given: 0

Director
Joined: 21 Aug 2005
Posts: 786

Kudos [?]: 28 [0], given: 0

### Show Tags

17 Nov 2005, 23:44
GMATT73 wrote:
E is not a LUCKY TWIN (no corresponding 0% among the answer choices) so no "Yukay" for you GSR.

See I've become dumb after taking the exam!

Kudos [?]: 28 [0], given: 0

VP
Joined: 22 Aug 2005
Posts: 1112

Kudos [?]: 121 [0], given: 0

Location: CA

### Show Tags

17 Nov 2005, 23:53
90%

678,463 is weird number..very few numbers will be its multiple.

it cannot be 100% as K can be 0 and thus 6^0 = 1.
678,463 is multiple of 1
_________________

Whether you think you can or think you can't. You're right! - Henry Ford (1863 - 1947)

Kudos [?]: 121 [0], given: 0

Director
Joined: 14 Sep 2005
Posts: 984

Kudos [?]: 215 [0], given: 0

Location: South Korea

### Show Tags

18 Nov 2005, 00:33
duttsit wrote:
90%

678,463 is weird number..very few numbers will be its multiple.

it cannot be 100% as K can be 0 and thus 6^0 = 1.
678,463 is multiple of 1

At first, I thought it should be (E) 100% because 678463 is an odd number and Z is an even number.

However, there is a hidden 1 as duttsit explained.

K can be 50 different numbers, and in 5 cases K is 0.

Therefore, 1 - 5/50 = 90%

(D) should be it.
_________________

Auge um Auge, Zahn um Zahn !

Last edited by gamjatang on 18 Nov 2005, 00:38, edited 1 time in total.

Kudos [?]: 215 [0], given: 0

SVP
Joined: 24 Sep 2005
Posts: 1884

Kudos [?]: 377 [0], given: 0

### Show Tags

18 Nov 2005, 00:35
well, let's see: because the second group contains the first 10 non-negative integers ...there's the case of 0 to be picked ..and the probability of picking 0 from this group is 1/10
The number 6.... (hik,don't remember) can only be a multiple of Z in case Z=1 , that is to say K=0 ..since K is the product of the two stated groups...the prob of K be 0 is 1/10 or 10%
So to let the conditon satisfied , the prob blah blah is 100%-10%=90%

Kudos [?]: 377 [0], given: 0

Director
Joined: 14 Sep 2005
Posts: 984

Kudos [?]: 215 [0], given: 0

Location: South Korea

### Show Tags

18 Nov 2005, 00:40
GMATT73 wrote:
gsr wrote:
Well, my probability skills is not one that i can boast of
Looking at this, the number 678,463 seems to be a prime number (atleast not divisible by (2, 3, 4, 6, 7, 8, 9, 11...).
Also, 6^k is even.
On the exam I will go for E) 100%

E is not a LUCKY TWIN (no corresponding 0% among the answer choices) so no "Yukay" for you GSR.

Yukay is really expensive!!!

However, what is LUCKY TWINS?
_________________

Auge um Auge, Zahn um Zahn !

Kudos [?]: 215 [0], given: 0

SVP
Joined: 24 Sep 2005
Posts: 1884

Kudos [?]: 377 [0], given: 0

### Show Tags

18 Nov 2005, 01:13
gamjatang wrote:

However, what is LUCKY TWINS?

for example: two answer choices X% and Y% , if X% + Y% =100% , they're lucky twins and possibly correct answer so pay much attention to these pairs. Those answer choices which can't find another choice to form lucky twins can be eliminated. Thanks to Matt for nice trick

Kudos [?]: 377 [0], given: 0

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16760

Kudos [?]: 273 [0], given: 0

Re: The purpose of this problem is to exploit a weakness used by [#permalink]

### Show Tags

27 Feb 2014, 14:21
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

Re: The purpose of this problem is to exploit a weakness used by   [#permalink] 27 Feb 2014, 14:21
Display posts from previous: Sort by