Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 02 May 2012
Posts: 10

What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
Updated on: 03 May 2012, 00:30
Question Stats:
67% (00:31) correct 33% (00:38) wrong based on 194 sessions
HideShow timer Statistics
What is the probability that two siblings, ages 6 and 8, will have the same birthday, assuming neither was born in a leap year? A. 1/133225 B. 1/365 C. 1/48 D. 1/14 E. 1/2 A. 1/133225  I thought this was the correct answer, because from what I understand if we want to find out the prob that BOTH siblings will have the same birthday is much higher than just 1/365. Even though they are independent events, which is 1/365 per time a child is born, in order for both of your child to have the same bday the odds presumably increases. Can someone please correct my logic. Thanks.
Official Answer and Stats are available only to registered users. Register/ Login.
Originally posted by iNumbv on 02 May 2012, 14:27.
Last edited by Bunuel on 03 May 2012, 00:30, edited 1 time in total.
Edited the question



Intern
Joined: 12 Feb 2012
Posts: 17
GPA: 4

Re: What is the probability that two siblings, ages 6 and 8 ... [#permalink]
Show Tags
02 May 2012, 14:44
The first sibling is born on a given day, that probably is 1/1. The probability of the second having a birthday on the same day is 1/365.
You have to think as the two as independent events. The probably of one person having a birthday on ANY date is 1/1, not 1/365. The second has to match.



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11970
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
02 Apr 2015, 12:50
Hi All, The explanation offered by pstrench is the most straightforward way of dealing with this question. The approach taken by iNumbv isn't 'wrong' so much as it's 'incomplete.' You CAN calculate the probability that two people are BOTH born on any individual day. eg. What is the probability that they are BOTH born on January 1st? (1/365)(1/365) Since we have to account for the FULL YEAR though, we would need to consider all 365 options. You don't really need to write them all out though, since you know that each is the same product. This gives us... (365)(1/365)(1/365) The first two parentheses 'cancel out', leaving us with.... 1/365 Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************



Manager
Joined: 18 Mar 2014
Posts: 232
Location: India
Concentration: Operations, Strategy
GPA: 3.19
WE: Information Technology (Computer Software)

Re: What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
04 Apr 2015, 10:17
EMPOWERgmatRichC wrote: Hi All, The explanation offered by pstrench is the most straightforward way of dealing with this question. The approach taken by iNumbv isn't 'wrong' so much as it's 'incomplete.' You CAN calculate the probability that two people are BOTH born on any individual day. eg. What is the probability that they are BOTH born on January 1st? (1/365)(1/365) Since we have to account for the FULL YEAR though, we would need to consider all 365 options. You don't really need to write them all out though, since you know that each is the same product. This gives us... (365)(1/365)(1/365) The first two parentheses 'cancel out', leaving us with.... 1/365 Final Answer: GMAT assassins aren't born, they're made, Rich Hi Rich , I am able to follow your solution till you consider both of them to be born on 1st Jan. So each has probability of having bday on 1st jan is = 1/365 Then why we should not multiply these two probabilities ?? as 1/365 * 1/365 I'm a bit confused here ... Aditya
_________________
Press +1 Kudos if you find this Post helpful



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11970
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
04 Apr 2015, 12:26
adityadon wrote: EMPOWERgmatRichC wrote: Hi All,
You CAN calculate the probability that two people are BOTH born on any individual day.
eg. What is the probability that they are BOTH born on January 1st?
(1/365)(1/365)
GMAT assassins aren't born, they're made, Rich Hi Rich , I am able to follow your solution till you consider both of them to be born on 1st Jan. So each has probability of having bday on 1st jan is = 1/365 Then why we should not multiply these two probabilities ?? as 1/365 * 1/365 I'm a bit confused here ... Aditya Hi Adiya, If you take another look at my explanation, you'll see that I DID multiply (1/365)(1/365)....This is the probability that 2 people are born on January 1st. Since there are 365 days in a normal year and since the question asks for the probability of two people being born on the SAME day (any day, not just on January 1st), we have to think about ALL 365 days. So there are 365 individual calculations that equal (1/365)(1/365). 365(1/365)(1/365) = 1/365 GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
Special Offer: Save $75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee www.empowergmat.com/
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************



Moderator
Joined: 22 Jun 2014
Posts: 1053
Location: India
Concentration: General Management, Technology
GPA: 2.49
WE: Information Technology (Computer Software)

Re: What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
22 Jan 2016, 09:38
probability of one person born on 1st january is = 1/365 probability of other being born on 1st january is = 1/365 probability of first AND second born on 1st january is = (1/365)*(1/365) now they can be born on 2nd jan OR 3rd jan OR 4th jan..... OR any day out of the 365 days of the year. hence probability = (1/365)*(1/365) + (1/365)*(1/365) + (1/365)*(1/365) ........ add 365 times = 365*(1/365)*(1/365) = 1/365
_________________
 Target  720740 http://gmatclub.com/forum/informationonnewgmatesrreportbeta221111.html http://gmatclub.com/forum/listofoneyearfulltimembaprograms222103.html



NonHuman User
Joined: 09 Sep 2013
Posts: 7248

Re: What is the probability that two siblings, ages 6 and 8 [#permalink]
Show Tags
12 Aug 2017, 22:02
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.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: What is the probability that two siblings, ages 6 and 8
[#permalink]
12 Aug 2017, 22:02






