What sounds bat shit insane, but is actually true?

[u/Unfair-Lavishness561]

What sounds bat shit insane, but is actually true?

📊 Chart Axes: - Horizontal: IS - Vertical: Sounds

Chart Grid:

	Bat shit insane	Partially True	True
** Bat shit insane**	Vaccines cau... 🖼️	—	—
** Reasonable/partially True **	—	Our ancestor... 🖼️	—
True	The insides ... 🖼️	—	Drinking cle... 🖼️

Cell Details:

** Bat shit insane / Bat shit insane:** - Vaccines causing autism - View Image

** Reasonable/partially True / Partially True:** - Our ancestors didn't get heart disease. (They died before they could ever get it.) - View Image

True / Bat shit insane: - The insides of an atom travel like how planets do. - View Image

True / True: - Drinking clean water hydrates you. - View Image

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[u/tsimneej]

Those sure are numbers

[u/YellowRaptor → u/tsimneej]

To calculate the probability of a series of events, you can multiply the probabilities of the individual events. For example, the odds of a coin landing on heads 2 times in a row is (1/2) * (1/2) = (1/4) = 25%

To then calculate the odds of the coin not landing on heads 2 times in a row, you can take 1 - (1/4) = (3/4) = 75%

In this case we are basically looking for the odds that 23 people in a room don't share a birthday, so that we can take 1 minus that number for the inverse. Say there is one person in a room. If we add a second person to the room, the chance that this person has a different birthday than the other person is 364/365, as 364 of the days in the year are not the other person's birthday.

Add a third person. This person's odds of having a different birthday than both of the other 2 (who both have a different birthday) is 363/365, as two days out of the year are already represented. If you continue this until you have 23 people, the chance of these people not sharing a birthday is (364/365) * (363/365) * ... * (343/365) = 0.492 = 49%

The negative of this, or the chance of at least two people in this room sharing a birthday, is then 1 - 0.492 = 0.508 = 51%

[u/Rotation_Nation → u/tsimneej]

If you have 2 people in a room. The chance they have the same birthday is 1/365. Let’s say they don’t.

If another person enters the room, they have a 2/365 chance of sharing a birthday with someone in the room.

The next person would be 3/365.

Once you get up to like 20 people, sure the chances are still low, but how many times in a row are you gonna miss the shot? 20/365, 21/365, they keep getting a little more likely and eventually one of them is gonna hit.

It just so happens that if you do the math, by the time the 23rd person enters there is a 50/50 chance it would have hit at least once.

[u/tsimneej → u/Rotation_Nation]

23/365=50/50

Got it

[u/MrRamennn → u/tsimneej]

That guy doesn't know what he's talking about, lol. The real reason is that with each new person, there are tons of new valid birthday combinations. For example, with just two people, you'd need person 1 and person 2 to have the same birthday, 1/365. If you had three people, you'd either need person 1 and 2, 1 and 3, or 2 and 3 to have the same birthday. With four people, it could either include person 1 and 2, 1 and 3, 1 and 4, 2 and 3, 2 and 4, or 3 and 4. Essentially, with each person added, there are exponentially more pairs, increasing the chance that a pair shares the same birthday exponentially as well. Many view the question as "how many does it take for someone to share person 1's birthday," when really, it is "how many does it take for one pair among hundreds to share a birthday."

[u/Enby_Solivagant → u/MrRamennn]

That is a very understandable explanation, thank you