David Lock

You ask someone 4 questions and each question has a choice of two answers. In total there are 2 correct answers (not in the same question btw).

What are the chances of someone getting both answers correct?

Doin' my ed in innit ta muchley.

davegtt

choice of two answers, in total there are 2 correct answers, obviously cant be to the same question, so are you saying 2 of the questions dont have a correct answer.

Question isnt quite clear enough

OllyK

So 2 questions have 2 incorrect answers and the other 2 each have 1 correct answer?

TelBoy

So two questions have 2 false answers, is that what you're saying?



I thought it first

OllyK

Assuming I have understood, you can ignore the 2 questions without a correct answer as they don't figure. So you now have two 50:50: scenarious so they have a 1 in 4 chance of getting both correct (0.5 x 0.5)

davegtt

No I would say there are 8 possible answers and only 2 are correct from 4 questions. although saying that both people will get 2 questions wrong so yeah your right. 50/50 chance of 2 people getting the right answer if Ive understood it correctly

edit, cant be, its 50% chance of someone getting each question right. so 25% chance of getting both right. then halfed for the chance of a second person doing exactly the same?!?!?!

so 1/8 or 12.5% chance.

PeteBrant

Ill be along later to give you the definitive answer, being the forum expert on probability.

davegtt

PeteBrant

4 questions. 2 question for each = 8 questions.

2 possible right answers in total.

2/8 =1/4 chance of someone getting both right.

TelBoy

Hold on. If the person answering HAS to answer all four questions, then obviously there is NO chance of him getting just the two correct answers. Or do you mean the two correct answers and two incorrect answers?


Here we go again

davegtt

Or 1/8 for 2 people getting them both right?

Clarebabes

Doesn't make sense.

TopBanana

The question isn't at all clear David!

However, I will say that the chance of getting any questions correct at all depends very much on whether the individual in question gets his Dad to do his homework for him

PeteBrant

I dont think he mentions two people answering does he?

But - if it were 2 people...

16 questions in total

4 possible correct answers..

4/16 = 1/4 - i think the odds are the same?

PeteBrant

or....

DO you disregard 2 of the questions because they have no right answer.

I.e. probabbility of getting a correct answer in two of the the questions = 0

Probabbility of getting correct answer in the two remaining questions = 2/4

50% chance of getting 2 questions right.

TelBoy

By Jove i think he's got it

David Lock

OK guys. Thanks a million btw. Some clarification which I have now received from daughter.

She is doing a unii psychology project. It involves young kids looking at an adult's eyes as an adult looks at a picture which is either a friend or a stranger to the adult (the child only sees the adults eyes, not the picture). The adult's eyes will show a recognition or not as he sees the picture of a friend or stranger. The idea is to see if the kid recognises this in the adult and is asked for a reaction as the adult looks at each of 4 pictures. So we need to try and establish what are the chances of the kid getting this randomly correct. So I guess it's 2-1 per picture and 16-1 for all 4 pictures? My daughter asked if the random chance could be expressed as a single number but I don't know what she meant? Hope this helps??? david

OllyK

Ok so there are 4 test pictures. The child can answer Recognition or not in each case and can be right or wrong in each case. So each of the 4 questions is a 50:50 so the chances of correctly getting all 4 tests correct is 0.5 x 0.5 x 0.5 x 0.5 = 0.0625

PeteBrant

Well the chance could be expressed as a percentage.

Given the experiement you have described. Then it may put a differen tspin on things. The odds of getting it "right" are no longer 50% in total - I think, because you are looking for a reaction in all picutures - not just the ones with people the adult recognises in means you have a 50/50 for each picture, which when you have 4 pictures = a 6.25 % chance of guessing the correct 2.


I think,....

Tel..help.

OllyK

If they get the 2 pictures correct that the adult recognises it also goes that guessed the adult didn't recognise the other 2 and so they actually get all 4 questions right.

David Lock

Thanks boys and my apologies for the slightly misleading first post. So looks like 16-1 whiuch is .0625.

Do I have to admit I got help

PeteBrant

Ah yup, that follows.

so a 6.25 chance of guessing all 4 pictures as being recognisable or not correctly.

TopBanana

The probability is 0.0625 but when she gets her results, it might be better to view each 50% chance as a seperate sample instead of grouping them into fours and analyzing that. The more samples she has, the greater the statistical confidence... which is in turn another probability

David Lock

All a great and speedy help and not a fecking troll in sight. Supa dupa

Luminous

iTrader: (3)

I started to think about this one, but have some more questions, sorry

The four pictures that the adults are going to be shown, I take it that 2 are of friends, and 2 are strangers then?

You also need to decide if you want to know about false positives? As an example lets say pictures 1 and 2 are friends of mine. 3 and 4 have no meaning to me. What constitues a positive test result?

Option 1:
Child looks into my eyes and correctly determins that when I look at pics 1 and 2 they are my friends. The fact that when I look at pics 3 and 4 the child incorrectly thinks that they are my friends is irrelevant?

Option 2:
The child must correctly tell you that when I look at pics 1 and 2 that they are my friends. The child must also tell you that when I look at pics 3 and 4 that they are not my friends.

Option 2 is much harder, and in my opinion the correct thing to be looking for. Effectively the child must get the right answer to each of the questions. They must tell when I look at a friend, and they must also tell when I look at someone whom I dont know.

If option 2 is what you are looking for, then the statisical probability of the child guessing all of the answers correctly is simply 0.5^4 (or 0.5x0.5x0.5x0.5) which works out at 1:16 or 6.25%

If option 1 is what you are after, then the questions asked when i am not shown a friendly face are meaningless. In fact, they are so meaningless they should not be included in your experiement (from my current understanding). Nevertheless, if option 1 is indeed what you are after you are only concerned with the child getting 2 random events correct, each with a 50% chance. In that case your answer is 25%

David Lock

Thank you Luminous. I have relayed your message to my daughter. So thanks from her as well

scunnered

iTrader: (1)

It reminds me of a question I remember as a child.
A man looks at a photogragh and says "Brothers and sisters I have none, but that man's father was my fathers son".
It wasn't easy trying to figure out who the man was looking at in the photo when you're only 8 years old.