Let $X=1,2,3,4,5$. Find the number of subsets of $X$ that contain at least one even number.

Step-by-step solution

1. Total subsets of a 5‑element set: $2^5=32$.
2. Subsets with no even number are formed only from the odd elements $1,3,5$: $2^3=8$ subsets.
3. Subtract: $32-8=24$ subsets contain at least one even number.
4. Hence the answer is $24$.

Concept tested: counting subsets via inclusion–exclusion

Published 13 October 2026 · How this solution was prepared and checked