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Puzzle: I have two children ...

Santino said:
There are three doors. Behind one is plane taking off. What is the chance that the goats behind the other doors are both male?
Click to expand...
You ask a goat (chosen at random) what the plane would do if it drew a black ball from the bag.
 
Santino said:
It's the difference between:

1. What is the probability of a two-child family having two boys?

and

2. What is the probability of a two-child family having two boys, given that we already know one of them is a boy?
Click to expand...

See, now those are different. The ones I quoted aren't.
 
I felt a disturbance in the force, as if a million people all cried out at once and were silenced.
 
I can't be arsed ploughing through the whole thread so I'll give my answer and people can tell me why I'm wrong.

According to the question we know only that...

1) There are two children.

2) One of the children is a boy

3) At least one boy was born on a Tuesday

I'll dismiss 3 as an irrelevance except that it gives rise to 2.

We know there are two children which would give the following possibilities.

i) Boy/Boy

ii) Boy/Girl

iii) Girl/Boy

iv) Girl/Girl

We can dismiss iv as we know at least one child is a boy

We can dismiss iii as being the same as ii

Therefore we have two possibilities Boy/Boy or Boy/Girl with equal probability so 50/50
 
I concur. The day of the childs birth is irrelevant and if used gives a wrong result.

The second child is either a) a boy
or b) a girl

Therefore 50/50
 
Similarly, if the month of the childs birth is given, July say. What answer would that give... 23/47ths.

23/47 does not equal 13/27. Clearly, there is a problem with using the childs date of birth to determine its sex.
 
rover07 said:
I concur. The day of the childs birth is irrelevant and if used gives a wrong result.

The second child is either a) a boy
or b) a girl

Therefore 50/50
Click to expand...
Right. So by the same logic:

Today I will either a) die
or b) not die

Therefore, it is 50/50 whether or not I die today. Oh noes! :eek:
 
longdog said:
If you're a cat in a box then yes. :p
Click to expand...
Only if the amount of radioactive material in my box has been chosen such that the probability of at least one atom decaying over the specific time period in question (today) is exactly 50/50. And therein lies rover07's problem. He is not considering the quantity of material, only the number of possible outcomes. Which is why he is wrong (as are you). :p
 
Im sticking to my own statistical analysis. Dont be bringing radioactive cats into this ...what day was the cat born on?:p
 
ymu said:
Only if the amount of radioactive material in my box has been chosen such that the probability of at least one atom decaying over the specific time period in question (today) is exactly 50/50. And therein lies rover07's problem. He is not considering the quantity of material, only the number of possible outcomes. Which is why he is wrong (as are you). :p
Click to expand...

I don't understand what you mean by quantity of material.

We know there is a second child and that the child could be either male or female with an equal chance of it being either.

Where's 'quantity' enter in to it?
 
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