Give a={a, b,c},how many subsets does a have including 0?

8 subsets

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There are n = 3 elements in the given set, so there are 2^n = 2^3 = 2*2*2 = 8 subsets. Those 8 subsets are listed below

{a,b,c}
{a,b}, {a,c}, {b, c}
{a}, {b}, {c}
{ }

The first row is the original set. Any set is a subset of itself.
The second row represents subsets with exactly 2 elements.
The third row represents subsets with exactly 1 element
The fourth row is the empty set which can be written as