How do you no how many subsets are in a set, and is there a formula

Question

amistre64 · Answer

you start counting

amistre64 · Answer

how many none are in it? {}
how many ones?
how many twos?
how many ....

anonymous · Answer

If the set has n elements then it has 2n subsets. Read more: http://wiki.answers.com/Q/How_many_subset_are_there_in_given_set#ixzz1hCg9BCtS

anonymous · Answer

finite set?  nice proof by induction

jamesj · Answer

That's 2^n subsets.

For example, consider the set A = {1,2}

Then the subsets are 
{}
{1}
{2}
{1,2}

that's 4, or 2^2

jamesj · Answer

the reason is given an element in A, it is either in or out of the subset.  1 is in or out; that's 2 possibilities; 2 is in or out, that's another 2 possibilities.  So there are 2x2 = 2^2 possibilities for the member of a subset, given a set with 2 members originally.

anonymous · Answer

ok thanks for the help