A set consist of 2n-1 element. What is the number of subsets of this set which contain at most n-1 elements?	Choices
A) 2^(2n-2)	B) 2^(2n) - 2	C) 2^(2n) -1	D) 2^(2n)	E) 2^(2n-1)
I took n=2 so total terms becomes 2n-1 = 3 and at most you can take n-1 = 1 term.   so the ans should be 3, but if you put n=2 in all the equations you wont get the ans. That means they have considered empty set as well, thus the total number of subsets with at most one is a1,a2,a3,0   so ans is 4.   put n=2 in all the equations , you will get 2^(2n-2)=4 hence 2^(2n-2).
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A set consist of 2n-1 element. What is the number of subsets of this set which contain at most n-1 elements?