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

[Fainne]

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.

OhTheManatee I have that cartoon in my study. I’m not very good at letting bad maths go unchallenged and this morning I am tired but I feel like I’ve fought the good fight. It’s not a work day today (thank goodness).

PowerslidePanda I am usually a primary school teacher. Patience is something I have a lot of experience with!

I was on here at 2.30am about to post that purple (and others!) were right when my tablet cut out and I had to go to sleep

I recently redid my maths A level and am now doing further maths for fun (!), got 100% on the stats paper in the A level (I’m proud of it, but I’m sure loads of you on here could do it with your eyes shut) and absolutely love stats. The stats part of further maths is by far my favourite bit.

Those of you on this thread with further stats qualifications such as lotsofoysters can you tell me that path you took? I’d love to do a maths and stats degree and work in statistics but as I already have a music degree I don’t think there’s the funding - and I’m not that young. But I don’t want to stop learning it! I don’t have great spreadsheet/ computer skills and I wonder if I need to address that. I’d love PMs on it if no one wants to derail this highly entertaining troll thread! Am now quite tired after not sleeping until 2.30am....

musicposy

You would probably be eligible for a student loan to take a second degree in maths and stats at the Open University. It's the STEM degree rules.

www.open.ac.uk/courses/fees-and-funding/equivalent-qualifications

@PurpleDaisies
You are amazingly patient.
And totally correct!

I'm glad I'm so late to this thread I don't feel obliged to get involved, it wouldn't be good for my blood pressure.

Shall we now move on to open the Box or Take the money?

@musicposy well done on the further maths! I loved further maths A-level too.

I did a maths degree followed by an applied statistics masters, then a PhD in applied stats. I got funding because I did the degrees straight from school. If you can't afford a traditional masters (they are extortionate these days) could you do an Open University course?

A lot of straight statistics courses are very computing heavy. You'd need to know/learn at least one programming language. It might be easier to tackle that by doing something more applied that uses a lot of statistics, like some of the social sciences or biological sciences.

The leap from A level statistics to degree level is pretty large - it isn't all probability problems! But the foundations built at A level are helpful.

@PurpleDaisies I did wonder if you might be a teacher! Not just the patience, but the way you were trying to explain it from various different angles.

I normally have more success with my classes.

Can’t be bothered reading it all but has it been agreed that it is 1/20 on each day regardless of the card? Surely ‘fate’ does not know which card you picked the day before?

Never have I been more frustrated reading a thread, and amazed at the patience of PurpleDaisies and other posters trying to explain.

I think the penny has dropped for the OP (or indeed they are the maths troll!), and they realise what an absolute idiot they have been, and rude. Probably slunk away in embarrassment to name change.

The MATHS troll??

Jesus, there’s a troll for everything!!

Who’s that aimed at?

Round of applause for @PurpleDaisies and @PotholeParadise for persevering at the start of this thread!

Nicely explained too.

I'm with Purple Daisys and I'm also a maths teacher.

The first few pages of the thread were getting me annoyed!

It would be 1/20.
You're asking about the odds of picking a card the second day GIVEN you picked it the first day, so 1/20.
It's different if you have a defined card the before the first pick. That would be 1/400.

My god this is like a car crash you can't stop yourself from looking at. @PurpleDaisies, total respect.

I think the issue is less “Can Mumsnet answer a question?” and more “Does the OP understand the question she’s asking and see why there’s a difference between two scenarios?”

And the answer to that is a resounding “No”!

(And I have a BSc. Hons in Maths in case she wants to get abusive!)

@PurpleDaisies
You are amazingly patient. And totally correct!

100% THIS.

It takes a special kind of stupid to not understand that before you start, that it's 20 times more difficult to pick the ace of diamonds twice running than it is to pick the same card (any card) twice running. If you only want to pick the same card twice, it doesn't matter what card you pick first!!! It's not rocket surgery!

I see the OP has disappeared now, probably out of embarrassment. Probably gone to start a thread saying she thinks there are 3 kinds of people in the world, those who can count and those who cant!

Bravo @PurpleDaisies

I lost patience once the OP started writing 'PMSL' (cringe) - but they did it whilst still being wrong. Great stuff

I have just skimmed through all the OP's posts. I can't believe someone can be so rude and yet so wrong.

I'm still wondering how OP thinking (incorrectly) that people can't calculate probability odds of picking the same card two days running equates to poker

But really this is an 'or' problem. Even If the odds are 1/400 of getting a card twice, there are 20 possible cards that you could get twice. To calculate or you add the odds together. 1/400 ×20 = 20/400 =1/20.

www.mysticbanana.com/in-a-tarot-deck-of-78-cards-what-are-the-odds-of-pulling-the-same-card-twice-in-a-row.html/

See answers from mathjoe and Bill A in this link. About 5th and 6th replies more or less - so you won't have to scroll too far.

You're welcome

If I'm wrong, I ain't the only one who's wrong!

But did you see the reply from 006 ?

It doesn't matter what card you pick first.
You just need the second to be the same as the first. So 1/20

If you actually care what card you get first, so you say you want the 3 of diamonds, then it is 1/20 x 1/20 = 1/400.

(I can't believe I'm getting sucked in.)

And OP, before you start having more of a go at quality of maths education, I have a maths degree from Cambridge.

With dice:
Chances of throwing double 6 = 1/36, but
Chances of throwing any double 1/6