



Thread Tools  Display Modes 
12312006, 02:50 AM  #1 
Scooby Newbie
Member#: 28488
Join Date: Nov 2002
Chapter/Region:
MWSOC
Location: Champaign, Il.
Vehicle:2000 Pierce Saber Fire Engine Red 
Odds of father and son having same birthday?
OT Math Geeks and stoners alike.
I'm curious: My father and I have the same birthday 30 years apart. What are the odds? Show you work, credit given to partial answers.
* Registered users of the site do not see these ads.

12312006, 02:54 AM  #2 
Scooby Specialist
Member#: 85805
Join Date: Apr 2005
Chapter/Region:
NWIC
Vehicle:The Strdr taketh and the Strdr giveth away 
1 in 365

12312006, 02:55 AM  #3 
Scooby Newbie
Member#: 129234
Join Date: Oct 2006
Chapter/Region:
NWIC
Location: Mount Vernon, WA
Vehicle:2002 Finally stage 2 Black 
too many variables.
If his mother was impregnated on Jan 1st then he would be born roughly 9 months and a week so if your mother was impregnated on Jan 1st then the odds greatly increase but it all depends on the woman and since his mother and your mother do not share any genetic traits(which does not necesssarily help in determining how long a baby will be carried) I think it's just luck of the draw but the odds do increase with both women getting pregnant in the same time frame( 2 weeks) 
12312006, 02:59 AM  #4 
Scooby Specialist
Member#: 74041
Join Date: Nov 2004
Chapter/Region:
TriState
Location: Atown PA
Vehicle:2006 2012 Weeestrom SV650 For sale 
My algaruthm(sp?) was roughly 18 hours off.
Father = 24 Me = 25 
12312006, 03:01 AM  #5 
Scooby Specialist
Member#: 32779
Join Date: Feb 2003
Chapter/Region:
South East
Location: The wilderness
Vehicle:'99 Tacoma LightOfTheWild.com 
1 in 365 if all the parents just regularly tried.
Unless you picked a date (Jan. 5th) and both sets went for the same date, that would be a much lower probability.  Stime187 does not think he's right. 
12312006, 03:02 AM  #6 
Scooby Newbie
Member#: 28488
Join Date: Nov 2002
Chapter/Region:
MWSOC
Location: Champaign, Il.
Vehicle:2000 Pierce Saber Fire Engine Red 
if it confuses you anymore: I was a preme I don't think my father was.

12312006, 03:13 AM  #7 
Scooby Specialist
Member#: 5659
Join Date: Apr 2001
Chapter/Region:
NWIC
Location: 127.0.0.1


12312006, 03:31 AM  #8  
Scooby Specialist
Member#: 21618
Join Date: Jul 2002
Chapter/Region:
SCIC
Location: southern California

Quote:
9 Months gestation, +2 weeks/4 weeks covers about 99% of the variance. So if you tried for, say, January 1st birthday and GOT PREGNANT on April 1st, you could have close to a 1:41.58 chance of hitting your target date. Of course the trick is getting pregnant on the right date. Assuming the female is ovulating on April 1 and you **** like crazy you could conceivably conceive on cue... That's a best case scenario. 

12312006, 03:36 AM  #9  
Scooby Specialist
Member#: 5659
Join Date: Apr 2001
Chapter/Region:
NWIC
Location: 127.0.0.1

Quote:
The odds certainly aren't any worse than that anyways * 

12312006, 03:40 AM  #10  
Scooby Specialist
Member#: 21618
Join Date: Jul 2002
Chapter/Region:
SCIC
Location: southern California

Quote:
The woman being fertile is a given, otherwise the odds shoot to Jesus levels. 1 : (every_other_child_ever_born  1) 

12312006, 04:42 AM  #11 
Scooby Specialist
Member#: 29059
Join Date: Nov 2002
Chapter/Region:
NWIC
Location: Rocky Point and Skyline
Vehicle:1992 Balvenie Portwood 
I say 1 in 365 as well.
Here's one for you... I was born on March 22nd, my wife on February 6th of the same year. She was born two weeks early and I was a full month late (poor mom!)... Feb 6th + 14 days = Feb 20 March 22nd  30 days = Feb 20 So in all likelihood, we were conceived within hours of each other despite a 6 week "age" difference! P03w 
12312006, 06:08 AM  #12 
Scooby Specialist
Member#: 71795
Join Date: Oct 2004
Chapter/Region:
NESIC
Location: Thread Improvement Task Force
Vehicle:2006 Impreza WRX5spd FREAKIN' BLUE!!! 
Father is born on a set date. Odds of son being born on the same date is dependent both on:
1.) 1/365.25 (leap year bishes) days of the year 2.) It being a boy (because it can be a girl too!)...(...suckas!) 1/2 1/(730.5) chance PS: Before people try and bring in "what if he has more than one son!" the question seems to imply (at least to me) that we're comparing "odds of father and son having the same birthday" both singular. If you want to do calculations with the average 2.47 kids per household or whatever it is be my guest . Last edited by Petrus; 12312006 at 06:13 AM. 
12312006, 08:45 AM  #13 
Scooby Specialist
Member#: 42714
Join Date: Sep 2003
Chapter/Region:
TriState
Location: Apalachin, NY
Vehicle:'07 BMW 335i E90 
Wow, OT is the suckorz at probability. If you flip a coin twice, what is the probability that it will be heads both times? 1/2? No, it's 1/2 * 1/2 = 1/4 (can have HT, TH, TT, HH). Similarly, the probability that two people (any two people) share the same birthday is 1/365 * 1/365 = 1/133225.

12312006, 09:00 AM  #14 
Scooby Newbie
Member#: 129234
Join Date: Oct 2006
Chapter/Region:
NWIC
Location: Mount Vernon, WA
Vehicle:2002 Finally stage 2 Black 
elucas, I had the same calculation earlier but it didn't seem correct.
365 x 365 = 133,225 but since it is essentially the same as flipping two coins wouldn't it be 1/66,612.5 or 2/133,225? I was thinking more in terms of 2 die with 365 sides(to make it easier in my head) but I think thats where I may have screwed up because then I got 365 positive results / 133,225 combinations which would end up giving you 1/365 which didn't make sense to me 
12312006, 09:05 AM  #15 
Scooby Newbie
Member#: 53066
Join Date: Jan 2004
Chapter/Region:
South East
Location: I guess a legend and an out of
Vehicle:work bum look a lot alike, daddy. 
Well, I'm leaning towards teh 1/365 answer, because my dad and I are the same day too, 27 years apart (12/28)

12312006, 09:14 AM  #16 
Scooby Specialist
Member#: 122980
Join Date: Aug 2006
Chapter/Region:
South East
Location: Raleigh, NC
Vehicle:2010 F150, 2013 CX5 92 Miata 15 TTF/PTF/E3 
Induced labor?

12312006, 09:28 AM  #17 
Scooby Specialist
Member#: 3400
Join Date: Jan 2001
Chapter/Region:
South East
Location: Boca Raton, FL
Vehicle:2013 Gojira 2007 Triumph Speed Triple 
What if somebody offered to bet that at least two people in your math class had the same birthday? Would you take the bet?
This question is more complicated than flipping a coin, because the chance of finding two people with the same birthday depends on the number of people you ask. If there were only one other person in your math class, you might be surprised to find out that she had the same birthday as you. If there were a pair of people with the same birthday in a class of 366 people, would you still be surprised? How large must a class be to make the probability of finding two people with the same birthday at least 50%? Let's forget about leap year when we solve this problem (no February 29 birthdays!) This way, we can assume that a year is always 365 days long. Also, let's assume that a person has an equal chance of being born on any day of the year, even though some birthdays may be slightly more likely than others. That will simpify the math, without changing the result signficantly. We'll start by figuring out the probability that two people have the same birthday. The first person can have any birthday. That gives him 365 possible birthdays out of 365 days, so the probability of the first person having the "right" birthday is 365/365, or 100%. The chance that the second person has the same birthday is 1/365. To find the probability that both people have this birthday, we have to multiply their separate probabilities. (365/365) * (1/365) = 1/365, or about 0.27%. Now, what about three people? The chance of the first and second person sharing a birthday is still 1/365. The first and third person might share a birthday instead. The probability of that is 1/365 as well. But what if the second and third person shared a birthday? And what if all three of them had the same birthday? Things are getting complicated fast. Four or five people would be even messier. Is there a simpler way? To solve the birthday problem, we need to use one of the basic rules of probability: the sum of the probability that an event will happen and the probability that the event won't happen is always 1. (In other words, the chance that anything might or might not happen is always 100%.) If we can work out the probability that no two people will have the same birthday, we can use this rule to find the probability that two people will share a birthday: P(event happens) + P(event doesn't happen) = 1 P(two people share birthday) + P(no two people share birthday) = 1 P(two people share birthday) = 1  P(no two people share birthday). So, what is the probability that no two people will share a birthday? Again, the first person can have any birthday. The second person's birthday has to be different. There are 364 different days to choose from, so the chance that two people have different birthdays is 364/365. That leaves 363 birthdays out of 365 open for the third person. To find the probability that both the second person and the third person will have different birthdays, we have to multiply: (365/365) * (364/365) * (363/365) = 132 132/133 225, which is about 99.18%. If we want to know the probability that four people will all have different birthdays, we multiply again: (364/365) * (363/365) * (362/365) = 47 831 784/ 48 627 125, or about 98.36%. We can keep on going the same way as long as we want. A formula for the probability that n people have different birthdays is ((3651)/365) * ((3652)/365) * ((3653)/365) * . . . * ((365n+1)/365). If you know permutation notation, you can write this formula as (365_P_n)/(365^n). That's the same as 365! / ((365n)! * 365^n). We've made some progress, but we still haven't answered the original question: how large must a class be to make the probability of finding two people with the same birthday at least 50%? We know that the probability of finding at least two people with the same birthday is 1 minus the probability that everybody has a different birthday, and we know how to find the probability that everybody has a different birthday for any number of people. The easiest way to find the right class size is to use a calculator to try different numbers in the formula. It turns out that the smallest class where the chance of finding two people with the same birthday is more than 50% is... a class of 23 people. (The probability is about 50.73%.) http://mathforum.org/dr.math/faq/faq.birthdayprob.html 
12312006, 09:35 AM  #18 
Scooby Specialist
Member#: 3400
Join Date: Jan 2001
Chapter/Region:
South East
Location: Boca Raton, FL
Vehicle:2013 Gojira 2007 Triumph Speed Triple 
http://www.suburbanchicagonews.com/n...DAY_S1.article
And baby makes three Naperville siblings share the same birthday ... but no, they're not triplets December 26, 2006 BY KATIE FOUTZ Staff Writer Nineyearold Ben Lueken already thought it was exciting to share a birthday with his younger brother. Matthew, 6, was born Dec. 5, 2000, three years to the day after Ben was born. Since then, when their interests aligned, they have held joint birthday parties and shared birthday cakes. Then their parents, Linda and John Lueken of Naperville, learned they were expecting a daughter. Her due date: Dec. 5, 2006. "Both me and my brother thought that (her birthday) would be on Dec. 5," Ben said. "But our mom and dad didn't. When it actually came, and they called our grandma from the hospital, we were jumping up and down on our beds." Beating 48 millionto1 odds  John checked with two statisticians  Gabrielle Lueken arrived naturally at 6:27 a.m. Dec. 5. Her two big brothers chose a stuffed cat and a dollandblanket combination as presents for her. "Our baby sister was a present," Matthew said. The Luekens insist this happened by pure luck. In 1997, Ben came a week late, and labor had to be induced. In 2000, Matthew came 10 days early but entirely on his own. On Dec. 4 this year, several people called Linda, a stayathome mom, to see if she was in labor. "'So, are you going to have that baby tomorrow?'" Linda said they'd ask. "'Or are you going to wait?' I said, 'Well, she's going to wait! I have nothing to do with it.'" John, the director of construction for McDonald's Corp., was leaving a leadership meeting Dec. 4 when he and his colleagues discussed the odds. "Most of the response has been, 'You need to go to Vegas,'" he said. "That, or play the lottery numbers." Linda has never heard of another family having three kids with the same birthday without being triplets. However, two cousins from Aurora and Montgomery were born on the same day  Aug. 26  this year at RushCopley Medical Center in Aurora. In the entertainment world, Britney Spears and Kevin Federline almost had two samebirthday children  their son, Jayden James, was born Sept. 12, two days shy of their son Sean Preston's first birthday. It did happen to actor Jeffrey Tambor, former star of "Arrested Development"  his daughter, Eve, was born Dec. 10, the same birthday as his 2yearold son, Gabriel. Linda said friends and family can't believe her children's triple birthday is even possible. "They're just blown away," she said. "I believe it was just meant to be." The boys are looking forward to sharing birthday parties with their new sister. They might even make some concessions about the theme. "You think you'll have all planes and trains?" John asked. "No, let's do some Barbie dolls," Matthew replied. 
12312006, 11:05 AM  #19 
Scooby Specialist
Member#: 68407
Join Date: Aug 2004
Chapter/Region:
South East
Location: Memphis
Vehicle:2005 92x Aero 2012 Outback 2.5i 6MT 
My fatherinlaw and brotherinlaw share the same birthday.

12312006, 11:21 AM  #20 
Scooby Newbie
Member#: 83039
Join Date: Mar 2005
Chapter/Region:
TriState
Location: Rochester, NY
Vehicle:2005 LegacyGT Ltd 5m ಠ_ಠ 

12312006, 11:25 AM  #21  
Scooby Newbie
Member#: 15376
Join Date: Feb 2002
Location: Bozo MT
Vehicle:'02 WRX Wagon '87 BMW 535is 
Quote:
As it is, Dec 5 is only significant because it was the day the first child was born. The other two are the coincidence... so its (1/365^2 = 1/133,225) and, of course, all of the other variables people have mentioned... if they were trying for Dec 5 (which they probably were, after the first two were born) the odds are much better. 

12312006, 11:26 AM  #22 
Scooby Specialist
Member#: 99777
Join Date: Nov 2005
Chapter/Region:
International
Location: North Dakota doesn't exist.

My two cousins (same family) have the same birthday either a year or two years apart.
My sister has the same birthday (same day) as her twin cousins, who's mother is my mothers sister. All born on December 18th, 1989. Same hospital, same room. Other oddities, the majority of my grandmothers grand children are born in the fall (most in October). There are 22 (including me) of them and I think only 3 are not fall birthdays. One more that I can think of is that myself and many of my friends are born on the 11th of a month. Every 11th we call around to see who it is. There are 8 of us who have this, none with the same birthday. 
12312006, 11:29 AM  #23  
Scooby Newbie
Member#: 3622
Join Date: Jan 2001
Chapter/Region:
MWSOC
Location: Chicago and beyond
Vehicle:2002 WRX Platinum Visa Metallic 
Quote:


12312006, 11:31 AM  #24 
Scooby Specialist
Member#: 120791
Join Date: Jul 2006
Chapter/Region:
TriState
Location: morris county
Vehicle:2014 xv dk 
thats pretty cool my mom and i have the same birthday like 15 years apart.

12312006, 11:34 AM  #25 
Scooby Specialist
Member#: 91407
Join Date: Jul 2005
Chapter/Region:
South East
Location: the souf
Vehicle:Ver. 2 WRX STi wagon but it's a bucket 
Hm.
My dad and his dad have the same birthday. My sister and our grandmother have the same birthday. 
Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
A GF of one of my friends is having a birthday get together on Friday. Most of her..  Mud Pig  OffTopic  53  07292004 11:26 AM 
Ice racing video of WRX and STI's having fun.  Mx5racer  Motorsports  6  02102004 01:22 PM 
Father names son "Version 2.0"  HappyEeyore  OffTopic  7  02032004 07:41 PM 
like father like son! :)  Benjamin Tang  Forester Forum  1  02152003 10:03 PM 
Do MY96 and MY98 have same body frame?  eicbal18  Interior & Exterior Modification  1  12282001 06:56 PM 