Question

满足条件{a}真包含于M包含于{a,b,c,d}的所有不同集合M的个数是几个.这道题该怎么算?

Answer 1

一共有七个

{a,b}

{a,c}

{a,d}

{a,b,c}

{a,b,d}

{a,c,d}

{a,b,c,d}