AQA GCSE Computer Science Paper 1 (1C), June 2025: Question 2

✅ Correct Answers

• L1: i Mod 5 = 0
• L2: Console.WriteLine("Free biscuit")
• L3: Console.WriteLine("Nothing free")

💡 Key Knowledge

• How Modulo works: i Mod n returns the remainder when i is divided by n . If i Mod n = 0 , i is an exact multiple of n .
• Order of conditions: A 20th stamp earns a cake, not a pastry or biscuit. Because 20 is a multiple of both 4 and 5, checking i Mod 20 = 0 must come first.
• Fall-through: The final Else catches all stamps where no reward is earned, requiring output: "Nothing free" .

🧠 Exam Technique

Read the specification carefully to identify exact required string outputs:

• Line above L1 already checks: If i Mod 20 = 0 (Free cake).
• Next branch outputs "Free pastry" (every 5th stamp) → L1 must check for multiples of 5.
• Branch ElseIf i Mod 4 = 0 needs the biscuit output in L2 → "Free biscuit" .
• The prompt requires exact strings: "Free biscuit" , "Free pastry" , "Free cake" , or "Nothing free" .

❌ Common Errors

• Using division ( / ) or Python syntax ( % ) instead of the VB.NET operator Mod .
• Writing an equality check with double equals ( == ). In VB.NET, comparison uses a single equals sign ( = ).
• Missing quotation marks around string literals inside Console.WriteLine(...) .
• Missing out the closing parentheses in method calls.

✅ Model Solution (VB.NET)

📐 Calculation Breakdown

1. Unit Prices:
   • Biscuits = £1.00 each
   • Pastries = £2.50 each
   • Cakes = £3.00 each
2. Formula:
   total = (biscuits * 1) + (pastries * 2.50) + (cakes * 3)
   (Note: multiplying biscuits by 1 can simply be written as biscuits ).
3. Data Type Note: Because pastries cost 2.50, the total value can be a decimal, so store it in a Double or Decimal variable if explicitly declared.

🧠 Examiner Guidance & Tips

• Prompt messages: You are allowed to include prompt strings (e.g. Console.WriteLine("Enter biscuits: ") ) or omit them and read directly into variables. Both score full marks.
• Explicit declarations: In GCSE mark schemes, explicit type conversions (e.g., Convert.ToInt32(...) ) and explicit Dim statements are not strictly penalised if omitted, but writing clean declarations is best practice.
• Case-insensitivity: VB.NET is case-insensitive, so console.readline() is accepted.

❌ Common Errors to Avoid

• Hardcoding inputs: Assigning fixed numbers rather than reading input from the user (e.g., writing biscuits = 5 instead of reading from console). This loses Marks A and B!
• Mixing up multipliers: Pairing £2.50 with biscuits or cakes instead of pastries.
• Missing the output step: Calculating totalValue correctly but forgetting to print it with Console.WriteLine() (loses Mark D).
• Repeated syntax errors: A repeated identical syntax mistake (e.g. missing closing bracket on every readline) incurs a DPT (Definite Penalty Treatment), capping marks at 3/4.