Common Mistakes and How to Avoid Them

This lesson identifies the most common mistakes that students make in OCR J277 exams and provides practical strategies to avoid them. Learning from others' mistakes is one of the most efficient ways to improve your exam performance.

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Mistake 1: Not Reading the Question Properly

The problem: Students rush into writing an answer without carefully reading what is asked. They answer a different question from the one set.

How to avoid it:

• Read the question twice before writing
• Underline the command word (state, describe, explain, discuss)
• Underline key technical terms
• Check how many marks the question is worth
• Check if the question asks for a specific number of points (e.g., "Give two reasons")

OCR Exam Tip: If a question says "Explain two reasons...", you need exactly two reasons, each with an explanation. Writing three reasons does not earn extra marks and wastes time.

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Mistake 2: Not Showing Working in Calculations

The problem: Students write only the final answer for calculation questions. If the answer is wrong, they get zero marks.

How to avoid it:

• Write the formula first
• Show each step of the calculation
• State the units (bits, bytes, KB, MB)
• Check whether your answer is reasonable

Example of good working:

File size = width x height x colour depth
         = 1920 x 1080 x 24
         = 49,766,400 bits
         = 49,766,400 / 8 = 6,220,800 bytes
         = 6,220,800 / 1024 = 6,075 KB
         = 6,075 / 1024 = 5.93 MB

Even if you make an arithmetic error, the formula and method marks are still available.

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Mistake 3: Confusing Similar Concepts

Commonly confused	Concept A	Concept B
RAM vs ROM	Volatile, read/write, stores running programs	Non-volatile, read-only, stores boot instructions
LAN vs WAN	Small area (building/site), high speed	Large area (country/world), lower speed
Lossy vs Lossless	Permanently removes data, smaller files	Preserves all data, larger files
Compiler vs Interpreter	Translates all at once, creates executable	Translates line by line, no executable
HTTP vs HTTPS	Unencrypted web protocol	Encrypted web protocol
Bit vs Byte	Single binary digit (0 or 1)	8 bits
ASCII vs Unicode	128/256 characters, English	149,000+ characters, all languages

How to avoid it: Create comparison flashcards for easily confused pairs. Test yourself regularly.

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Mistake 4: Writing Too Much for Low-Mark Questions

The problem: Students write a full paragraph for a 1-mark question, wasting valuable time.

How to avoid it:

• 1 mark = 1 sentence (or even a few words)
• 2 marks = 2 sentences or bullet points
• 4 marks = a short paragraph with 4 distinct points
• 6+ marks = structured extended response with paragraphs

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Mistake 5: Incomplete Code Answers

The problem: Students forget closing keywords, miss variable initialisations, or write incomplete programs.

Common code mistakes: