# I Can you calculate probability with infinite sets?

1. Aug 11, 2017

### gamow99

Suppose set A is defined as the even integers and set B is defined as for every even integer there are two odd integers, like so: {2,3,3,4,5,5,6,7,7 .... }

Can you calculate that the probability of choosing an odd number is 66%?

2. Aug 11, 2017

### Orodruin

Staff Emeritus
Not without an appropriate probability distribution.

3. Aug 11, 2017

### gamow99

Don't know what you mean.

4. Aug 11, 2017

### Orodruin

Staff Emeritus
In order to give a probability for something to happen you need to specify the probability distribution for the possible outcomes.

5. Aug 15, 2017

### Zafa Pi

Then you should not have used the Intermediate classification for your thread. There is no natural probabilistic method for selecting a member from a countably infinite set.
If you choose uniformly from {2,3,3',4,5,5', ... 10^20) then the probability of selecting an odd is very close to 2/3. The uniform distribution is natural for a finite set, but there is no such for the infinite case.