To think that this sum is super simple

[PeerieBreeks]

and can't understand how so many people on Facebook have it so completely wrong (and can justify it to themselves).

Without adding your reasoning, tell me what you think the answer is.

3EyedRaven - I'm not sure your version makes sense. Are you saying Monty opens a single door (with a goat behind it)? That still leaves 98 doors behind which the car might lie.

Your example would work if Monty opens 98 doors showing goats - so now there are two doors still closed, the one you initially picked and one other that Monty chose not to open. In that scenario, then, yes that other door has a 99/100 chance of being the door with the car. It's obvious that you almost certainly should swap.

I think in 3Eyed version, Monty picks a door and offers you to swap with him. But it only works if Monty has to pick the door with the car if one of the 99 doors you didn’t pick has the car behind it.

Ah, that makes sense - and is equivalent to my scenario (mine just makes it explicit that all but one goat is now eliminated).

Yes, Monty knows which door has the car before you start, so if he opened all the other 98 doors they would all be goats. I simplified it in my head by having him eliminate the other doors and then offer to swap, but I agree it demonstrates the point better by opening the 98 doors first, and the logic is the same ( 1/100 and 99/100 rather than 1/3 and 2/3)

I have not RTFT and I see we are now onto game shows but he needs to stop fucking about with this horse and just buy a cat.

They're $20 and he won't manage to sell because it's a cat and will have fucked off out when they buyer comes round.

This means he's now spent $20 on a fucked-off-out cat, in addition (and subtraction) to the hokey-cokey horse and he's no good for a round in the pub because he's broke.

Meanwhile, I have snuck behind Monty's door, stolen the car and replaced it with the horse.

$20 up

Forget about Monty opening a door—that's just a distraction. Basically he's offering you the choice of keeping your original door, or swapping it for all the other doors (whether there are two or 200).

it might help to understand if you imagine there are one hundred doors.
h ha yes I've read that explanation online too, and it's the only way I can get my head round it.

DC marvel I thinkthis sort of problem is actually a lot easier for young children because they have not got the higher understanding which complicates problems for adults.

I'm a bit wobbly when it comes to probability problems but I found it illuminating to compare the 3 door scenario as given with Monty in the know about where the car is with the case where Monty doesn’t know what’s behind the doors.

In the latter case if Monty happens to open the door on a goat and invites the contestant to swap, there is no advantage in doing so. The probability of getting the car is the same for swapping and not swapping. (This is the same as the intuitive answer.)

Comparing these two situations (Monty in the know versus not in the know) and seeing how the latter case had to be modified to produce the former gave me a better understanding of what was going on and why swapping was an advantage in the former case.

Has anyone been following the literal zombie thread, ie the woman that was declared dead by a 'drama llama'? It has been picked up by the sun - and at the end of the article it mentions this thread. So hello to any Sun readers that have popped over for a look!

The information is too limited. It ignores bank charges. After they have been applied it is about $17.60 profit.

People are saying it is a math question. No it isn't. Primarily, it is a logic question.

A man buys two horses and sells them for $10 more each time, so makes $20. The fact that the horse are the same and the asking prices rises in between is irrelevant.

I could see that straight away after retiring at 5:30 am and getting up again at 9:00 am. Others may have more difficulty when they are wide awake. But never mind.

Oh god I saw this and got 20. I saw so many saying 10 that I thought I'd missed something and felt like a total idiot. I showed my 12 year old nephew and he also got 20 within about 5 seconds after having read it... baffled too as to how so many people get it wrong.

Oh gosh even reading some of these responses has me confused ! I'm hopeless at maths so the more complex ways to solve this have me lost.

I simply worked it out starting from 0 and use an imaginary overdraft

Starts at 0
Buys for 60
Now has -60
Sells for 70
Now has + 10
Buys for 80
Now has -70
Sells for 90

So -70 + 90 = 20

I teach Functional Maths.
This perfectly illustrates the reasons why my job is not straightforward.

$10 up

Nearly 1 week in, and 500 posts later & people are still getting it wrong!

The man lost 40$ he started with 60$ only had 20$ in the end.

So easiest way to figure it out is to imagine you have a wallet with $100 in it.
$100 - $60 = $40 left in wallet...bought horse
$40 + $70 = $110 in wallet... sold horse
$110 - $80 = $30 left in wallet... buying the same horse
$30 + $90 = $120 in wallet...sold same horse
$120 - $100 = $20 dollars profit

The man lost 40$ he started with 60$ only had 20$ in the end.

I know you're joking, but I love this picture.

He breaks Even.. How can you justify it's two separate transactions he buys the same horse back.

A transaction is "money changing hands (in exchange for something)". This happens twice, so two transactions.

No, born, it happens four times. 2 purchases and 2 sales.

Oops!

Profit of $30 💰