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Original poster

to ask if you can answer a question re probability (Maths question)

999 replies

Fainne · 24/01/2020 00:23

So, say I have 20 cards in a pack.

I pick one. It's the Ace of Diamonds let's say for argument's sake.

I then pick another one out of the same pack of 20 cards the following day.

Am I correct in saying that the odds of me picking the same card is a multiple of the single odds?

So 1/20 x 1/20 = 1/400

?

Because I've someone telling me the odds are still 1/20 that I'll pull the same card.

OP posts:
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8
StatisticallyChallenged · 26/01/2020 10:58

If you randomly chose which door to stay with - e.g. by flipping a coin - then you would have a 1/2 chance of choosing the right door.

That is not the same as thinking you have a 1/2 chance of winning by sticking with your door.

chomalungma · 26/01/2020 10:58

I just watched the show, you do know there is no swap. Right

TBF - that does seem true. This is Monty Hall himself talking about the problem - and apparently he offers money instead or what's behind the door.

But the Monty Hall problem itself - if it was a show like that, then you should always swap.

chomalungma · 26/01/2020 11:02

This has the opportunity to be a really good street scam.

Just take 3 cards. Make sure you know where the winning card is.
Get someone to gamble £1 or whatever.

They put their money on the card they think it is.
You show a card it isn't.
Ask them if they want to swap or stick.

If they win, they double their money.

Chances are a lot of people won't swap because they haven't heard or understood the situation.

So you're quids in. Eventually

mummmy2017 · 26/01/2020 11:04

The doors may have a 1/3 and 2/3.
But the show will either classed as car or no car. That is 1/2.

chomalungma · 26/01/2020 11:05

But the show will either classed as car or no car. That is 1/2

Please - I really have to go out. Grin

But before I go, I might buy a lottery ticket. I might win or I might not win.
What are the odds of me winning the lottery?

lotsofoysters · 26/01/2020 11:10

The doors may have a 1/3 and 2/3.
But the show will either classed as car or no car. That is 1/2.

You have a 10% chance of dying during a medical procedure you need to have. The medical statistics classify you as either dead or alive after the operation, only two options. Therefore it's 50/50 that you survive, is it?

TabbyStar · 26/01/2020 11:12

Why is this thread still going? 😂

SerendipityJane · 26/01/2020 11:13

Why is this thread still going?

I did say it was a metaphor Grin

StatisticallyChallenged · 26/01/2020 11:20

Why is this thread still going

Because lack of logic really frustrates people who get stats!

PestyMachtubernahme · 26/01/2020 11:23

@iseetodaywithanewsprintfray did you make it through the night?

I presume you are currently both Wink

OffToTheMoon · 26/01/2020 11:24

As you @'d me, I'm going to try once more.
You say One door may have a higher probability of a win but if your only playing one game then you can just choose the door you like.
Read that back - they are your own words.
One door may have a higher probability of a win*
Therefore NOT 50/50 even though there are only 2 doors. One is weighted.

mummmy2017 · 26/01/2020 11:25

On medical records they do list who died and who walked away.
On X day 100 operations were performed ,
From a cyst to heart surgery.
Only 2 people died on the given day.
So 98% stats .
You might then break down the stats on each op, but 98 of the 100 walked out of the hospital.

OffToTheMoon · 26/01/2020 11:26

Although of course, the word 'may' should be replaced with 'does' (as explained many times earlier and i think you do agree with the 1/3 2/3 odds).

mummmy2017 · 26/01/2020 11:28

Moon on the form for the show.
The executive fills in a report.
Did the contestants win the show or lose the show?
No one cares about weighted doors.
They just want to know if they gave away a car

KidLorneRoll · 26/01/2020 11:42

I love this thread. People getting probabilty utterly wrong but being totally convinced there are right is always hilarious.

OffToTheMoon · 26/01/2020 11:45

Mummy, you're now confusing your apples with your pears. You are talking about a different thing now. The first thing is the chances of winning a car 1/3 vs 2/3 which i think we all agree on (regardless of how many games you play). The second (unrelated to the first) thing is the producers recording win vs lose.

chomalungma · 26/01/2020 11:46

I wonder what the statistics would show the producers if everyone stuck to their original choice?

mummmy2017 · 26/01/2020 11:51

But I have always been on about the 10 pears.
Ten wins in a row.
Your the lot who keep talking about a single apple.

chomalungma · 26/01/2020 11:54

The producers very much want to know the probabilities at the start.

They would also have calculations of what would the outcome be over a series of say 100 shows if half the people swapped.

Because they need to know the economics of it. How many cars are they likely to give away

mummmy2017 · 26/01/2020 11:57

Thank you for seeing my point about wins in a row.
Yes it is different to a contestants odds.

chomalungma · 26/01/2020 12:06

What point are you trying to make?
Just answer one simple question?
What is the best strategy to win?
Just to win this game.
You are on the show right now.
You picked a door.
I reveal a goat.
What should you do and why?

Lweji · 26/01/2020 12:10

But the show will either classed as car or no car. That is 1/2.

You either get statistics or you don't. What do you think are the odds of you not getting it? 50%?

mummmy2017 · 26/01/2020 12:16

Ok, as the producer I want to know the chances of 10 wins in a row?

As a contestant on one show only.
The doors are weighted 1/3 , 2/3.
But when my family ask I either win the show or lose the show.

Playing the game ten times in a row.
I have odds of 1/1024 to win.
I need to win each show to progress.
If I lose on show 7 , I can't get to show 10.

ItsGoingTibiaK · 26/01/2020 12:21

I love it when people like @mummy2017 arrive thinking they’ve come up with something no-one’s thought of before, and everyone else just doesn’t understand how smart they are.

This is really, really old, well-understood maths. The whole game is designed around the maths - and the fact that it’s counter-intuitive. That’s what makes it interesting.

The game also relies on human emotion. People think “but what if I swap boxes and get it wrong - I’ll have thrown away a car that I already practically owned!” - again, that’s what makes it interesting.

Yes, sometimes you’ll win by sticking, but you’re more likely to lose. No-one has ever said you’re guaranteed to win by swapping, because you’re not. You’re just more likely to win - it’s the smart choice, but it’s still a gamble, with the odds in your favour.

Casinos and bookies rely on people like you, who think they know better. They don’t care if sometimes your gamble pays off, because the whole system is designed in their favour. Over the course of the millions of bets they take, the statistics guarantee they take in more than they pay out.

chomalungma · 26/01/2020 12:23

Ok, as the producer I want to know the chances of 10 wins in a row

Actually as the producer, I want to know how many cars will have been won at the end of 10 shows.

That's the difference. I don't care if there were 10 wins in a row.
I care about how many cars I am likely to give away.