On Friday before our gender reveal, he sent us this mathmatical analysis of baby odds to venture his guess.
We thought it was really funny, so we asked his permission to post it so others could enjoy his creative scientific work as well. :)
BABY ODDS
A BRIEF STUDY OF “THE PELISHEK PROBLEM.” OR “HOW I LEARNED TO STOP WORRYING AND LOVE THE BOMB”
BY KARL STAVEMONE BABY
Okay... so the odds of having a boy or girl are 50/50, right? So, when you conceived (ha, sex) Zoe, there was a 50% chance that she could have been a boy.
So what is this saying? If 100 women had babies about 50 of them would be girls, and 50 would be boys.
TWO BABIES
NOW... What are the odds of having two kids - each of them girls?
Well, conceiving (ha, sex again!) is an independent task. Meaning it doesn't matter what happened before, each time you conceive (do it) the odds are still 50%.
SO... to find the probability of two independent events occurring in sequence, find the probability of each event occurring separately, and then multiply the probabilities. In math words... when two events, Z and S, are independent, the probability of both occurring is:
P (Z and S) P (Z) P (S)
So, the probability of Zoe, Z, being a girl:
p[Z] (.5);
Probability, of Sophia Justice, S, being a girl:
p[S] (.5);
Probability of both of them being girls:
p[Z and S] p[Z] p[S]
0.25
Printed by Mathematica for Students
2 gender.nb
So there’s only a 25% that if you have two kids they will both be the same sex. Weird, right?
So, what does this mean? That if 100 women all had two babies: 25 of them would have two girls, 25 would have two boys, and 50 would have a mix of boys and girls.
THREE BABIES
So, since you are being mysterious and not letting anyone know what you’re having, I’m left to guess.
Well, it’s a coin toss as to what happened when you conceived (BOOM). So what’s the likelihood that you’ve got a girl on the way? 50%!!
I feel like we’ve covered that part. BUT...
Remember we're not looking at individual cases. We’re looking at your whole family and asking the question, “What are the odds that a family could have three children, and all of them are girls?”
The odds of the same result occurring three times in a row is pretty low.
Think about doing a coin toss three times. It seems more likely that you will have a mix of heads and tails instead of three heads with no tails. (In this example, tails are penises).
So we go back to our formula with independent tasks, and this time throw in one more variable... G for girl.
P (Z and J and G) P (Z) P (J) P (G)
So... the probability of having a girl:
p[G] (.5);
The probability of having three girls, and no boys:
p[Z and J and G] p[Z] p[J] p[G]
0.125
So, the odds of having three girls in a row is 12.5%.
So what does this mean? That if 100 women had three children each, about 13 of them would have 3 girls.
Printed by Mathematica for Students
gender.nb 3
SO WHAT’S YOUR POINT??
So... you’ve got a group of 100 women. Each of these women had three babies. Only about thirteen of the women have three girls.
Meaning there are 87 other women who have AT LEAST ONE boy.
My conclusion: You are having a boy.
It HAS to be. I mean the odds of having three children with AT LEAST ONE boy are 87.5%. But that’s just a guess...
TO THE CENSUS DATA!!!
Do census figures back up my theory?
OF COURSE:
.
See the bottom there. That means in the US 12.1% of three-children families have all girls. EVEN LESS THAN WHAT I PREDICTED. SO... you’re having a boy.
THE END ###
(By the way: If I am wrong, ignore this.)
Printed by Mathematica for Students
3-Children_Families
Ii 14.151915 Actual
12.596 Predicted
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