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Chapter 2 — Chapter 2 — Number Systems

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Topic 1 · pp. 25–31 · Free

Number Systems and Conversions

Source: CS 9, Unit 2, pp. 25–31

📘Easy summary

Base (radix) = number of digits. Decimal base 10 (0–9); binary base 2 (0, 1); octal base 8 (0–7); hexadecimal base 16 (0–9, A–F). Decimal → other base: repeatedly divide by the base, write remainders bottom-to-top: 25₁₀ = 11001₂ = 31₈ = 19₁₆. Other base → decimal: multiply each digit by base^position and add: 1011₂ = 8+0+2+1 = 11. Binary ↔ octal by groups of 3 bits; binary ↔ hex by groups of 4 bits (1111 1010₂ = FA₁₆).

⭐Key points

  • Remainders read upward.

🔬Diagram

Decimal → binaryDivide by 2Note remainderRepeat until 0Read remainders upward

🌿Real-life example

13 → 1101₂.

💡Exam tip

  • Valid binary contains only 0 and 1.

✅Quick check

1. Valid binary:

2. Hex digits:

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