Grendel
Member
I've forgotten all my stat-math.
Here's my problem:
In a population of 20 million people I know that 53 people have the surname 'X'. (I need to know random values, ignoring family and tribal connections)
If I reach into the people-bucket and pluck out one person, then I calculate the chances of that person being X are (20,000,000 / 53) = 370,000:1 against. To be statistically confident of plucking out X I would have to scoop out 370,000 people at once.
But if I can only scoop out 20,000 per dip, then what are the odds of 'X' being in that 20K scoop? I work this out at
A: (370,000 / 20,000) = 18.5
Now what are the chances of a random 20K scoop containing two 'X's?
B: (18.5 x 18.5) = 340:1 or 6.8 million people.
Now what are the chances of them both having the same initial?
C: (340 x 26 x 26) = 230,000:1 or 4.6 billion people.
I would have to scoop the bucket 230,000 times (with 20K scoops) or I would need a population of 4.6 billion people to be confident that two 'X's have the same initial?
Is this correct?
Cheers Greg
Here's my problem:
In a population of 20 million people I know that 53 people have the surname 'X'. (I need to know random values, ignoring family and tribal connections)
If I reach into the people-bucket and pluck out one person, then I calculate the chances of that person being X are (20,000,000 / 53) = 370,000:1 against. To be statistically confident of plucking out X I would have to scoop out 370,000 people at once.
But if I can only scoop out 20,000 per dip, then what are the odds of 'X' being in that 20K scoop? I work this out at
A: (370,000 / 20,000) = 18.5
Now what are the chances of a random 20K scoop containing two 'X's?
B: (18.5 x 18.5) = 340:1 or 6.8 million people.
Now what are the chances of them both having the same initial?
C: (340 x 26 x 26) = 230,000:1 or 4.6 billion people.
I would have to scoop the bucket 230,000 times (with 20K scoops) or I would need a population of 4.6 billion people to be confident that two 'X's have the same initial?
Is this correct?
Cheers Greg