A complete, no-prep, single-topic worksheet on binary and denary conversions for GCSE Computer Science, mapped to AQA 8525 (3.3.1 Number bases and 3.3.2 Converting between number bases). Students work through a fully worked conversion in each direction — binary to denary and denary to binary, for values from 0 to 255 — then complete guided conversions, independent practice, ordering practice, and four exam-style questions with mark allocations, including the classic trap: always write all 8 bits, and check the place-value headings first. Includes an extension page (how many values 8 bits can hold, and what a ninth bit adds) plus a full answer key with every conversion worked, so marking takes minutes or students can self-mark. Print pages 2–3 for the class. 25–35 minutes, no equipment needed. Ideal for a cover lesson, homework, or targeted revision of data representation.