AI-verified
Every contribution passes a two-pass AI referee. The community confirms or challenges it here — so correctness is checked once and kept honest over time.
Community problem · Combinatorics · Pigeonhole
Socks in the dark
A drawer holds red socks and blue socks, jumbled together. In the dark, how many socks must you take out to be certain of having a matching pair? Prove your answer is exactly right.
Stuck? A gentle nudge
No hints for this one.
Your working
Check your full solution
Attach photos of your pages (up to 3) or one PDF — or check what you typed above. Lemma reads the work and verifies the reasoning, not just the answer.
Your first check today doesn't need an account.
Your photos and PDFs are read once and not stored — only the transcription is kept.