Question

The number of non-empty proper subsets of a set containing 7 elements is______

• A. 128
• B. 127
• C. 126
• D. None of these

Answer 1

The correct option is C 126

Number of proper subsets of a set containing $n$ elements is $2^n-1$
So, a set containing $7$ elements will have $2^7-1=128-1=127$ proper subsets
But one of these proper subsets is a null set.
Hence, number of non zero proper subsets will be $127-1=126$