Q4. If S and T are two sets such that S has 21 elements, T has 32 elements, and S T has 11 elements, how many elements does S T have?
n(S) = 21
n(T) = 32
n(S T) = 11
n(S T) = n(S) + n(T) - n(S T)
n(S T) = 21 + 32 - 11
n(S T) = 53 - 11
n(S T) = 42
Hence, the set (S T) has 42 elements.