1,000 lockers. 1 key. Minutes to escape. 🗝️ Watch the 3-minute video free, then teach linear vs binary search with a ready-to-print pack: Teacher Guide, 100-mark worksheet and full marking scheme. 🧠 The video says “10 comparisons.” The real answer is 9. Can your students spot why? Zero prep. Cambridge, IB, AP and University CS.