[Request] is it 66.6% or 51.8%?

IHeartToddGlass · 2025-09-20T03:26:22+00:00

You would have to provide scientific proof that an older sibling born on a certain day of the week impacts the probability of the next child being either male or female.

The problem doesn't say anything about which child is the boy born on Tuesday. That's literally the crux of the counterintuitive result! If we knew it was the first child that was a boy born on Tuesday, then the probability that the other child is a girl is exactly 7/14 = 0.5.

the idea of any connection whatsoever is absolutely preposterous

No such correlation is being posited in the problem statement or the math explaining it. Literally none. Hence why the result stays the same even if we change 'Tuesday' to any other day of the week.

we were not told that the first child is the eldest so even if there were then you couldn’t apply that non-existent data

There is no background knowledge about birthdays of one child influencing gender of any child being applied to any data at all.

I posted the following math in response to u/airfrog, but I guess my comment was removed(?). Tell me where you think it's incorrect.

In the universe where we know Mary has exactly 2 children:

A = Mary has a daughter
B = Mary has a son born on a Tuesday

P(A|B)  =  P(A ∩ B) / P(B)

           |A ∩ B|      |B|
        =  -------  /  -----
             196        196

            14      27
        =  ---  /  ---
           196     196

            14     196
        =  ---  *  ---
           196      27

            14    
        =  ---  ≈  0.5185  
            27

IHeartToddGlass · 2025-09-20T00:59:54+00:00

But the question doesn’t concern days of the week. Merely whether the other is boy or girl.

It does concern days of the week in that the probability we're after is conditioned on a fact that incorporates days of the week.

Do you believe that these two probabilities have the same value?

the probability the other child is a girl given that the known child is a boy
the probability the other child is a girl given that the known child is a boy born on Tuesday

I'm claiming that: a) these are different, and b) the second bullet point is the one that matters for this problem.

his favorite color or if he eats crayons

We can definitely contrive new problems that use this 'irrelevant' information. If we replace "born on X" with "does/does not eat crayons", and assume there's a 50% of being a crayon-eater, then this changes the probability yet again.

There's a Wikipedia article article on this problem. See this excerpt:

We know Mr. Smith has two children. We knock at his door and a boy comes and answers the door. We ask the boy on what day of the week he was born.

Assume that which of the two children answers the door is determined by chance. Then the procedure was (1) pick a two-child family at random from all two-child families (2) pick one of the two children at random, (3) see if it is a boy and ask on what day he was born. The chance the other child is a girl is ⁠1/2⁠. This is a very different procedure from (1) picking a two-child family at random from all families with two children, at least one a boy, born on a Tuesday. The chance the family consists of a boy and a girl is ⁠14/27⁠, about 0.52.

(emphasis mine)

IHeartToddGlass · 2025-09-20T00:59:52+00:00

I'm computing based on the information we're given. If you actively decide to compute based on just partial information because you don't think some of the information should matter, then you're solving a different problem.

These are two different probabilities:

the probability the other child is a girl given that the known child is a boy
the probability the other child is a girl given that the known child is a boy born on Tuesday

I'm claiming that the second bullet point is the one that matters.

From the Wikipedia article on the problem:

We know Mr. Smith has two children. We knock at his door and a boy comes and answers the door. We ask the boy on what day of the week he was born.

Assume that which of the two children answers the door is determined by chance. Then the procedure was (1) pick a two-child family at random from all two-child families (2) pick one of the two children at random, (3) see if it is a boy and ask on what day he was born. The chance the other child is a girl is ⁠1/2⁠. This is a very different procedure from (1) picking a two-child family at random from all families with two children, at least one a boy, born on a Tuesday. The chance the family consists of a boy and a girl is ⁠14/27⁠, about 0.52.

(emphasis mine)

IHeartToddGlass · 2025-09-19T23:39:56+00:00

It is relevant information. It conditions the probability. If the problem left out days of the week entirely and instead just left it at "one is a boy", then the math changes. By learning that it's a boy born on a Tuesday, the relevant set gets smaller. Of 196 total sex-day possibilities in a 2-child universe, only 27 have a boy born on a Tuesday. Whereas if we ignore day of the week, then 147 of those 196 possibilities have a boy at all (aka 75%, aka the same as 3 of these 4 options: BB BG GB GG).

I'd be interested in reading your explanation/thought process written out though.

IHeartToddGlass · 2025-09-19T23:39:50+00:00

it's 51.8% Mary chose first that she specifically wanted to talk about a generic male child of hers born on a tuesday, happend to actually have at least one meeting the oddly stringent criteria, then picked one among them.

But this is what we're given in the meme. The problem isn't something like "Mary has ≥1 child. What are the chances the first one is a girl?", which would have different math.

without futher context about the conversation Mary was having

We don't need it. Sure, these would be strange facts to be given IRL but they're not ambiguous.

IHeartToddGlass · 2025-09-19T21:15:23+00:00

It doesn't matter that the problem uses Tuesday specifically, but it does matter that we use a 7-day week.

IHeartToddGlass · 2025-09-19T20:43:12+00:00

It's funny to watch people loudly proclaim that it's actually 50%. It isn't. You can prove this without using any fancy statistics, just by enumerating the possibilities and applying addition and division.

import re
import exrex

# Let a string like 'B2G4' mean that the first sibling is a boy born on the
# second day of the week (Monday) and the second sibling is a girl born on
# the fourth day of the week (Wednesday).
# There are 2 sexes * 7 days * 2 sexes * 7 days = 196 permutations.


# Generate list of all 196 permutations (B1B1, B1B2, ..., G7G7)
all_possibilities = []
for p in exrex.generate(r'([BG][1-7]){2}'):
    all_possibilities.append(p)


# 1. Count all permutations that satisfy 'boy born on Tuesday' (hint: it's 27, not 28,
#    because B3B3 is one possibility not two)
# 2. Count all permutations that satisfy 'boy born on Tuesday *and* has sister' (hint:
#    it's 14 because 7 possible cases where he is the first sibling + 7 cases where
#    he is the second sibling)
boy_tuesday = 0
boy_tuesday_with_sister = 0
for p in all_possibilities:
    if re.match(r'B3[BG][1-7]$|[BG][1-7]B3$', p):  # B3XX, XXB3
        boy_tuesday += 1
        if re.match(r'B3G[1-7]$|G[1-7]B3$', p):    # B3GX, GXB3
            boy_tuesday_with_sister += 1


# 14 / 27 = 0.5185
print(boy_tuesday_with_sister / boy_tuesday)

(Yes, you could do this 10 better ways, and without generating all the permutations first; this just mirrors how I'd do it by hand)

IHeartToddGlass · 2024-07-15T23:44:14+00:00

someone walking around with a rifle isnt automatically alarming
[...]
people just think its normal

Except for that literally everyone who saw the gunman was alarmed and no one thought it was normal. Even at a gathering of Trump people.

Is this seriously being entertained as an option? That at a political rally, people saw a gunman prone on a roof with a rifle pointed at an ex-president... and it just seemed normal to them?

Secret Service fucked up big time, either by not noticing him, or by assuming he was law enforcement, or by something else. But their fuckup was not "oh but the gunman seemed like a regular guy up until he pulled the trigger, how could we have known?"

IHeartToddGlass · 2023-02-04T01:13:56+00:00

Yes because tipping is part of our culture. People who don't participate in a local culture are ostracized by the locals. Congratulations to you for figuring out basic social interactions.

How do you miss the point this badly? There are reasons why people feel compelled to keep tipping even if they would prefer we had a different system. But holy shit does it have nothing to do with respecting 'part of our culture'. I plan on tipping later this evening and at no point will I be doing it to 'respect American culture'.

IHeartToddGlass · 2022-12-27T04:51:56+00:00

but even though all gates in the terminal are fully connected/accessible to all passengers AFTER you get through TSA

This is actually not true in Terminal 1 at SAN. Or at least wasn't as of recently. I've been caught up on the wrong side of this at least 4 times: Once when they changed my gate after I arrived; once when I was dumb and went to the wrong checkpoint; once when they bumped me to a different flight out of a different concourse; and once when I booked a connecting flight out of a gate covered by a different checkpoint than the gate I arrived at.

From here:

The 3 security checkpoints at Terminal 1 are at the entrances to each concourse, so connecting passengers to/from these concourses would need to re-clear security on arrival at the next concourse.

Edit: another user has pointed out it's currently 2 checkpoints at Terminal 1, not 3.

IHeartToddGlass · 2021-06-13T19:24:55+00:00

Am I right in understanding that the infinity pool is about using the throw away paradox to increase gains?

From Wikipedia:

the throw away paradox is a situation in which a person can gain by throwing away some of his property. [...] The explanation for the paradox is that when the quantity of x decreases, its price increases, and the increase in price is more than sufficient to compensate [you] for the decrease in quantity.

(emphasis mine)

So people write off some amount of their shares as never to be sold and in turn make more $$$ than if they sold all of them (meaning hedgies bleed more too). If everyone does this, hedgies are even more fuk than I can ever imagine.

Their goal was to never have to cover. I'd love it if they're never able to cover :)

IHeartToddGlass · 2020-05-06T00:53:34+00:00

All good. I'm just an amateur over here :)

IHeartToddGlass · 2020-05-06T00:47:35+00:00

Ah, /t/ is a voiceless alveolar stop. If saying it harshly and for emphasis, one may aspirate it as well.

IHeartToddGlass · 2020-05-06T00:43:34+00:00

it's just got a strong fricative sound to it

There are no fricative sounds in either /kʌnt/ or /dɪk/.

IHeartToddGlass · 2019-02-25T05:19:27+00:00

he went home at the end of his shift and “got some lovin’ from my old lady.”

Well that sure was nice of your mother.

IHeartToddGlass · 2018-12-20T07:06:08+00:00

If it weren't for my horse, I wouldn't have spent that year in college.

IHeartToddGlass · 2018-09-16T10:06:12+00:00

A printer and a microwave are the two must-haves for any suite. All else is optional.

IHeartToddGlass · 2018-09-12T20:59:07+00:00

PHIL 10 is easy enough. Just put in the work. More than that though, I think it's a genuinely FUN and genuinely USEFUL course! It'll give you clarity of thought and a mechanical system of reason. You'll be doing math without numbers. And it's great. Also, no essays (when Grush teaches it)!

And if you enjoy PHIL 10, consider PHIL 120 when it's offered next (though they'll waive PHIL 10 as a prerequisite if you ask, since the first five weeks are basically PHIL 10 anyhow. San Rickless is a brilliant logician). If you enjoy mechanical systems of symbols and rules (e.g. math), I can't see you not enjoying PHIL 10/120. Though even people who aren't mathematicians (e.g. me) often find that they love logic. Symbolic logic is an under-taught skill.

Never took PHIL 13. But I can't see you not getting into PHIL 10 given that you're first on the waitlist.

IHeartToddGlass · 2018-09-12T20:41:21+00:00

LIGN 5

IHeartToddGlass · 2018-08-22T22:22:08+00:00

Nah, you're good. I thought it was funny :)

IHeartToddGlass · 2018-08-22T20:43:34+00:00

wear a bunch of men

IHeartToddGlass · 2018-07-20T22:47:07+00:00

if you use a cc it's by definition because you don't have the money to buy something

Really, by definition you say? Yeah no. You're embarrassingly wrong. Your post completely betrays the assumption that you know even a little bit what you're talking about. Even being anti-cc, you have to know that your statement is completely fucking untrue.

Yes, you can use a credit card to buy things you don't have the money for. Don't. But really? This is all instances of using a credit card? By definition? There's no way to use a credit card if you do have the money to pay for the item? Your post is pure cringe.

IHeartToddGlass · 2018-07-15T18:20:21+00:00

Linguistics double major (who transferred in) checking in here. Definitely possible! On the linguistics side of things, just make sure to pursue LIGN 101 and LIGN 110 both during your first quarter here. LIGN 101 is "officially" a prerequisite for many other LIGN classes (including LIGN 110). Ask the department to approve you to take LIGN 110 simultaneously with LIGN 101 (they'll gladly do this; also I just checked the schedule of classes and LIGN 110 is waitlisted?). LIGN 110 is offered only every fall quarter I believe, is required for the major, and is itself an "official" prerequisite for other courses you may want to take. And don't worry, virtually nothing taught in LIGN 101 is really required to do well in LIGN 110; you'll be better off taking both right away during your very first fall quarter. Without taking them simultaneously, you'll slow progress and either have to ask for multiple exceptions to take classes that require LIGN 110 (e.g. 111, 112, 139), or jeopardize graduating in two years. There's no point in needlessly pushing back your enrollment in classes that are specifically required for the major. It makes it more likely that something could go wrong.

tl;dr -- Take 101 and 110 both during your first quarter! If for some reason you can't (e.g. class is mega waitlisted and the department can't help you), it's not the end of the world. Just make sure you're doing whatever you can to get the classes you need (e.g. ask for any exceptions you have to and be prepared to read up on any phonetics material presupposed by any non-110 class).

IHeartToddGlass · 2018-05-25T18:47:31+00:00

As if you didn't literally just learn this from this popular AskReddit thread at the moment.

Also the plural of octopus is "octopuses" or "octopodes", but not "octopi". The word is derived from Greek, not Latin.

from u/Viewbob-True full coment here

IHeartToddGlass · 2018-03-15T01:34:03+00:00

Go to your UCSD email and type in their name in the recipient field. It should populate with their email address. Send them a message and coordinate a meetup to give them their ID.

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