calculate the elements of set B if it has 254 subsets

Answer 1

for a set of n elements, the number of subsets is 2§n

2^n = 254

solve for n ,
BUT, since the number of elements must be a whole number, I suspect a typo, or else the question is bogus.

2^8 = 256
2^7 = 128

Answer 2

I guess if you discount B itself and Ø, then that leaves 254 "proper, non-null" subsets.