Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 07 Jul 2015, 20:25

### 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

# I know this is not typically a hard one but I have a

Author Message
TAGS:
Manager
Joined: 19 Sep 2005
Posts: 110
Followers: 1

Kudos [?]: 5 [0], given: 0

I know this is not typically a hard one but I have a [#permalink]  10 Nov 2005, 19:39
I know this is not typically a hard one but I have a question about it:

A fair die has sides labeled w/ 1, 2, 3, 4, 5, 6. If the die is rolled 4 times, what is the probability that on at least 1 roll, the die will show 6?

Now, I'd like to know why you HAVE to solve by looking at it from the probability of NOT getting a six. In other words...why can't you add 1/6 4 times? When is it key to go with probability of not getting what you are trying to get, rather than solving for the probability of getting it?

Many thanks
Director
Joined: 27 Jun 2005
Posts: 513
Location: MS
Followers: 2

Kudos [?]: 37 [0], given: 0

Re: Rolling a die [#permalink]  10 Nov 2005, 23:04
Jennif102 wrote:
I know this is not typically a hard one but I have a question about it:

A fair die has sides labeled w/ 1, 2, 3, 4, 5, 6. If the die is rolled 4 times, what is the probability that on at least 1 roll, the die will show 6?

Now, I'd like to know why you HAVE to solve by looking at it from the probability of NOT getting a six. In other words...why can't you add 1/6 4 times? When is it key to go with probability of not getting what you are trying to get, rather than solving for the probability of getting it?

Many thanks

Jennif102,

the die rolling is a independent event so the total probability will be the multipication of probability of each event.

and the case you are refering where using 1/6 as the probabiltiy of getting 6 .....1/6*1/6*1/6*1/6 .. is the probabiltiy of getting 6 in each event not getting at least one six.

but in the question the probability of at least one 6 is asked .....so in 4 rolls you may have 1 six or 2 six or 3 six ...or all 4 six ......so the best way is to 1 - probability of None= probability of at least one.....otherwise you have to consider the cases all the case

1six3Nonesix+2six2Nonesix...and so on

hope it helps....
Manager
Joined: 12 Mar 2005
Posts: 65
Location: Milton Keynes UK
Followers: 2

Kudos [?]: 5 [0], given: 0

Cool explanation Jonny009.
_________________

The ability to focus attention on important things is a defining characteristic of intelligence.
--by Robert J. Shiller

SVP
Joined: 28 May 2005
Posts: 1740
Location: Dhaka
Followers: 6

Kudos [?]: 77 [0], given: 0

i will do it as

1/6^4 +2/6^4+ 3/6^4+ 4/6^4

= 1/6^4 ( 1+2+3+4)

= 10/6^4
_________________

hey ya......

Manager
Joined: 19 Sep 2005
Posts: 110
Followers: 1

Kudos [?]: 5 [0], given: 0

Senior Manager
Joined: 07 Jul 2005
Posts: 405
Followers: 3

Kudos [?]: 23 [0], given: 0

Here you go:

P(xxxx) + P(6xxx) + P(66xx) + P(666x) + P(6666) = 1

P(6xxx) + P(66xx) + P(666x) + P(6666) = 1 - P(xxxx)

Since each occurance is an independent event.

P(xxxx) = P(x1) * P(x2) * P(x3) * P(x4)

The probability of not getting a 6 is 5/6

P(xxxx) = (5/6)^4

Hence,

P(6xxx) + P(66xx) + P(666x) + P(6666) = 1 - (5/6)^4
Similar topics Replies Last post
Similar
Topics:
I know this one has been discussed many times, but I would 5 28 Apr 2007, 07:02
I'm having a hard time w/absolute value. OA: B 1 01 Apr 2007, 14:14
One more hard one before I go and be merry! I will post 3 24 Dec 2006, 08:12
I know this one is pretty simple but I am pretty weak with 3 10 Oct 2006, 10:34
I know this one has been posted before by Kevincan but i 15 10 Aug 2006, 11:10
Display posts from previous: Sort by

# I know this is not typically a hard one but I have a

 Powered by phpBB © phpBB Group and phpBB SEO 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®.