Year 11 CAIE Computer Science: Unit Test Mock Paper Walkthrough | CAIE 计算机科学单元测试模拟卷解析

📚 Year 11 CAIE Computer Science: Unit Test Mock Paper Walkthrough | CAIE 计算机科学单元测试模拟卷解析

This walkthrough provides a step-by-step explanation of a mock unit test for the CAIE IGCSE Computer Science course. Each question targets a key syllabus area, allowing you to self-assess and identify topics for revision. Use the detailed solutions to deepen your understanding of binary manipulation, logic, data transmission, programming concepts and more.

本解析逐步讲解一份专为CAIE IGCSE计算机科学设计的单元模拟测试。每道题都紧扣考纲重点领域，帮助你进行自我评估并锁定需要复习的主题。通过详细的解答，你可以加深对二进制运算、逻辑电路、数据传输、编程概念等核心知识的理解。

1. Binary to Denary Conversion | 二进制与十进制转换

Question: Convert the denary number 201 into an 8-bit binary number. Then convert the binary number 10010110 back into denary.

问题：将十进制数201转换为8位二进制数。再将二进制数10010110转换为十进制数。

Answer – 201 in binary: 11001001
10010110 in denary: 150

答案 – 201的二进制：11001001
10010110的十进制：150

To convert 201, repeatedly divide by 2 and record the remainder at each step: 201 ÷ 2 = 100 R 1, 100 ÷ 2 = 50 R 0, 50 ÷ 2 = 25 R 0, 25 ÷ 2 = 12 R 1, 12 ÷ 2 = 6 R 0, 6 ÷ 2 = 3 R 0, 3 ÷ 2 = 1 R 1, 1 ÷ 2 = 0 R 1. Reading the remainders from bottom to top gives 11001001.

转换201时，反复除以2并记录每一步的余数：201 ÷ 2 = 100 余 1，100 ÷ 2 = 50 余 0，50 ÷ 2 = 25 余 0，25 ÷ 2 = 12 余 1，12 ÷ 2 = 6 余 0，6 ÷ 2 = 3 余 0，3 ÷ 2 = 1 余 1，1 ÷ 2 = 0 余 1。从下往上读取余数即得到11001001。

For the reverse conversion, write the place values above each bit: 128 | 64 | 32 | 16 | 8 | 4 | 2 | 1. For 10010110 the bits set to 1 correspond to 128 + 16 + 4 + 2 = 150. Always check that the most significant bit is correctly placed.

反向转换时，在每一位上方标出位权：128 | 64 | 32 | 16 | 8 | 4 | 2 | 1。对于10010110，值为1的位对应128 + 16 + 4 + 2 = 150。务必确保最高位的位置无误。

Tip: A common mistake is writing the binary from top to bottom instead of reversing the remainders. Practise with smaller numbers first to build confidence.

小贴士：常见错误是把余数从上往下写出，而忘记倒序。建议先用较小的数字练习以建立信心。

2. Hexadecimal and Binary | 十六进制与二进制

Question: Convert the hexadecimal number AF into an 8-bit binary number and then write its denary value.

问题：将十六进制数AF转换为8位二进制数，并写出对应的十进制值。

Answer: Binary = 10101111, Denary = 175

答案：二进制 = 10101111，十进制 = 175

Treat each hex digit separately: A₁₆ = 10₁₀ = 1010₂, F₁₆ = 15₁₀ = 1111₂. Putting them together gives 10101111. To confirm the denary value, add the place values: 128 + 32 + 8 + 4 + 2 + 1 = 175. In hexadecimal notation, A is the fifth letter, representing 10, and F is the sixth, representing 15.

分别处理每个十六进制数字：A₁₆ = 10₁₀ = 1010₂，F₁₆ = 15₁₀ = 1111₂。组合在一起便得到10101111。验证十进制值时，将位权相加：128 + 32 + 8 + 4 + 2 + 1 = 175。在十六进制表示中，A是第五个字母代表10，F是第六个字母代表15。

When working with hex, always expand each digit to exactly 4 bits. For numbers less than 16, add leading zeros to maintain the 4-bit group. This ensures accurate conversion.

处理十六进制时，每个数字务必扩展为恰好4位二进制。对于小于16的值，需在前方补零以保持4位一组，从而确保转换准确无误。

3. Binary Addition and Overflow | 二进制加法与溢出

Question: Add the two 8-bit unsigned binary numbers 10101101 and 01111001. Show your working and state whether an

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