Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 24 May 2017, 17:51

### 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

# If 7 distinct car accidents happened during 7 days, what is

Author Message
TAGS:

### Hide Tags

Director
Joined: 23 Apr 2010
Posts: 581
Followers: 2

Kudos [?]: 86 [0], given: 7

If 7 distinct car accidents happened during 7 days, what is [#permalink]

### Show Tags

07 Jun 2010, 03:34
2
This post was
BOOKMARKED
00:00

Difficulty:

(N/A)

Question Stats:

80% (01:44) correct 20% (01:33) wrong based on 3 sessions

### HideShow timer Statistics

If 7 distinct car accidents happened during 7 days, what is the probability that all the accidents happened on a particular day?

Official solution:

[Reveal] Spoiler:
OMEGA = 7^7
A = 7
P(A) A/OMEGA = 1/(7^6)

I don't understand the formula for counting the sample space. Your inputs/explanation would be very appreciated.

Thanks.
Manager
Joined: 04 May 2010
Posts: 87
WE 1: 2 yrs - Oilfield Service
Followers: 12

Kudos [?]: 120 [0], given: 7

### Show Tags

07 Jun 2010, 04:09
In general, the number of ways that "m" objects can be distributed into "n" boxes is n^m (When the objects and boxes are distinguishable, and a box can be empty) I've attached a little reference chart for you to remember the formula for these kind of problems. For the GMAT I wouldn't bother deriving them - just remember them.

So distributing the 7 boxes into the 7 days needs 7^7 ways.

It must be clear to you that if all 7 happened on the same day, it could happen in 7 ways, (since it depends on which day this happened)

Prob = 7 / 7^7 = 1 / 7^6
Attachments

File comment: Here's a nice little chart for these kind of repetition problems.

Combinatorics.jpg [ 18.18 KiB | Viewed 4185 times ]

Director
Joined: 23 Apr 2010
Posts: 581
Followers: 2

Kudos [?]: 86 [0], given: 7

### Show Tags

07 Jun 2010, 06:05
Current Student
Status: Everyone is a leader. Just stop listening to others.
Joined: 22 Mar 2013
Posts: 960
Location: India
GPA: 3.51
WE: Information Technology (Computer Software)
Followers: 171

Kudos [?]: 1611 [0], given: 229

### Show Tags

01 Aug 2013, 09:22
As I a remember there is one formula for distribution of n objects to r people, that formula consider all cases of distribution of the objects in chunk of 0 , 1 , 2 .. so on.

Formula = (n+r-1)C(r-1) (bcz i think accidents can happen or not happen on any particular day or even multiple accidents can happen) thus this formula qualifies to find all such cases.

13C6 = 1716

desirable cases are 7.

thus Prob = 7/1716

I hope i am right.
_________________

Piyush K
-----------------------
Our greatest weakness lies in giving up. The most certain way to succeed is to try just one more time. ― Thomas A. Edison
Don't forget to press--> Kudos
My Articles: 1. WOULD: when to use? | 2. All GMATPrep RCs (New)
Tip: Before exam a week earlier don't forget to exhaust all gmatprep problems specially for "sentence correction".

Current Student
Joined: 06 Sep 2013
Posts: 2005
Concentration: Finance
Followers: 68

Kudos [?]: 643 [0], given: 355

Re: If 7 distinct car accidents happened during 7 days, what is [#permalink]

### Show Tags

10 Dec 2013, 08:24
nonameee wrote:
If 7 distinct car accidents happened during 7 days, what is the probability that all the accidents happened on a particular day?

Official solution:

[Reveal] Spoiler:
OMEGA = 7^7
A = 7
P(A) A/OMEGA = 1/(7^6)

I don't understand the formula for counting the sample space. Your inputs/explanation would be very appreciated.

Thanks.

7C6/7^7=1/7^6

Pretty straightforward
Cheers
J
Intern
Status: Researching for Schools
Joined: 21 Apr 2013
Posts: 20
Location: United States
GMAT 1: 640 Q45 V34
GMAT 2: 730 Q49 V40
WE: Project Management (Computer Software)
Followers: 0

Kudos [?]: 7 [0], given: 76

Re: If 7 distinct car accidents happened during 7 days, what is [#permalink]

### Show Tags

31 Jan 2014, 13:41
jlgdr wrote:
nonameee wrote:
If 7 distinct car accidents happened during 7 days, what is the probability that all the accidents happened on a particular day?

Official solution:

[Reveal] Spoiler:
OMEGA = 7^7
A = 7
P(A) A/OMEGA = 1/(7^6)

I don't understand the formula for counting the sample space. Your inputs/explanation would be very appreciated.

Thanks.

7C6/7^7=1/7^6

Pretty straightforward
Cheers
J

Hi jlgdr,

Can you please explain why 7C6 in numerator.

Thanks
Current Student
Joined: 06 Sep 2013
Posts: 2005
Concentration: Finance
Followers: 68

Kudos [?]: 643 [0], given: 355

Re: If 7 distinct car accidents happened during 7 days, what is [#permalink]

### Show Tags

31 Jan 2014, 14:03
vivekisthere wrote:
jlgdr wrote:
nonameee wrote:
If 7 distinct car accidents happened during 7 days, what is the probability that all the accidents happened on a particular day?

Official solution:

[Reveal] Spoiler:
OMEGA = 7^7
A = 7
P(A) A/OMEGA = 1/(7^6)

I don't understand the formula for counting the sample space. Your inputs/explanation would be very appreciated.

Thanks.

7C6/7^7=1/7^6

Pretty straightforward
Cheers
J

Hi jlgdr,

Can you please explain why 7C6 in numerator.

Thanks

Sure. Each accident can happen in each of the 7 days.
We want the scenario in which all happen in the same day
Therefore, since all accidents will happen in the same day then we only need to pick in which day out of the 7 days will all the accidents happen

So 7C1 = 7C6 = 7

Hope its clear
J
Re: If 7 distinct car accidents happened during 7 days, what is   [#permalink] 31 Jan 2014, 14:03
Similar topics Replies Last post
Similar
Topics:
What is the units digit of 7^20? 9 08 Feb 2017, 19:45
1 What is the tens digit of 7^381? 3 09 Aug 2016, 11:43
11 What is the tens digit of 7^1415? 6 01 Nov 2016, 15:29
1 What will be the remainder when 13^7+14^7+15^7+16^7 is div.. 3 02 Dec 2013, 10:38
48 If 7 workers can build 7 cars in 7 days, then how many days would it 19 16 Feb 2017, 01:24
Display posts from previous: Sort by