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.

[PotholeParadise]

So, how many ways are there of throwing two (six-sided) dice so they land with the same number?

P.S. Got higher maths quals than you. That's fun.

[Spamantha]

What are the chances of me getting the same card twice = 1/400 (because there are 400 possible outcomes)
Dont you start too!

20 of those 400 outcomes are the same card being pulled twice.

[Fainne]

Okay geniuses.

What are the odds that I pick one card on day one, replace it, pick another card on day 2 and another on day three. Replacing the card each day.

What are the odds that I'd pick the same card 3 days running (assuming a pack of 20 different cards).

I really want a particular card to come out.

[PurpleDaisies]

sleep you’ve not quite got it.

What are the chances of me getting the same card twice = 1/400 (because there are 400 possible outcomes)

Twenty of those outcomes give you matching cards. The probability of getting the same card twice is 20/400 or 1/20.

The thing that changes it is whether you want two of the same particular card twice.

It’s easier to think about with the dice example. Do you need two matching dice or two sixes? Then the probability is 1/6 or 1/36 respectively.

[Fainne]

20 of those 400 outcomes are the same card being pulled twice.

Lol

[PurpleDaisies]

If you want the a particular card on all three days, it’s 1/20 x 1/20 x 1/20 = 1/8000

[Fainne]

This is basic Maths!

[Fainne]

No Purple it's not. Whatever card I want has no bearing on the probability of me getting the same card 3 days running. Unless I'm fucking psychic or some shit. It doesn't matter what card I want.
I asked the probability of getting the same card 3 days in a row. I didn't specify a card. Read.

[PurpleDaisies]

I agree it is basic maths.

You still don’t appear to be able to correctly calculate the probability of two dice displaying matching numbers correctly.

[PurpleDaisies]

You are changing the question again.

You said...I really want a particular card to come out.

I assumed you wanted the probability of that one card coming out three days in a row.

[Fainne]

Ok Purple. So what are the odds of me picking the same card 2 days running?

[PurpleDaisies]

For the new question you’re asking, There are twenty different cards so twenty out of the 8000 possible combinations will have matching cards.

20/8000 = 1/400

[Fainne]

You're not really getting this are you? What I want doesn't change the probability lol

[PurpleDaisies]

That was three days running.

The odds of picking the same card two days running are the same as they were every other time I’ve explained it.

[Fainne]

Finally! So the answer is 1/400. Thank you. You got there eventually.

[daisypond]

Purple is spot-on.

[PurpleDaisies]

What you’re not getting is that specifying the cards you want changes the possibility of getting what you want.

I want matching cards two days running. 1/20
I want matching aces of clubs two days running 1/400.

[Fainne]

Bless.

[msmith501]

Late to the thread but can't the example of two coins be used e.g. if I have two coins and throw them, the possible combinations would appear to be:

H + H
H + T (heads and tails)
T + H
T + T

Which suggests to me that the probability of throwing a Head with on coin is 1 in 2. The individual probability of throwing a head with the second coin is also 1 in 2. I think we all agree on that.

So, there seems to be the question in the thread of the probability of two of the same card / dice number / coin side occurring vs two of the same when the card / number of dots / side of coin is specifically named in advance. Maybe the coin example is flawed for some reason but Using the above, the odds of getting two of the same (either Heads or tails) appear to be 2 out of 4 (H + H or T + T) where as the odds of (say) H + H specifically appears to be 1 in 4.

[Fainne]

I never specified a card I wanted.

[PurpleDaisies]

If you’re not specifying which cards you want, to get any two that match, it’s 1/20. To get any three that match, it’s 1/400.

If you can’t see it with dice with all the different possibilities drawn out for you, you just won’t get it.

What on earth did you learn on that higher certificate course?

[PotholeParadise]

What are the odds that I pick one card on day one, replace it, pick another card on day 2 and another on day three. Replacing the card each day.

6840/8000 (which simplifies to 342/400).

What are the odds that I'd pick the same card 3 days running (assuming a pack of 20 different cards).

I really want a particular card to come out.

Do you mean that you only want the chance that you will get the Seven of Hearts three times? Not the chance that you might get any heart card thrice?

1/8000

[OhTheManatee]

Drawing cards on 3 days:
Probability of same card every day: 1/400
Probability of ace of diamonds every day: 1/8000
Given ace of diamonds picked on day 1, probability of same card each day: 1/400
Given ace of diamonds picked on day 1 and day 2, probability of same card every day: 1/20

[PurpleDaisies]

Going back to the dice where you said the possibility of getting two matching numbers was 1/36^5...
1/36^5 = 1/60466176
That means that if you were correct, the dice would only show matching numbers about once every 60 million rolls. Does that pass the common sense test for you?

[PotholeParadise]

I never specified a card I wanted.

Oh for heaven's sake.

You're the one who keeps using the word "want" in the first place!