Arithmetic in Python

Lesson Overview

Unit: Python Programming Basics (Lesson 5 of 6)
Key Stage: KS4 (GCSE) / KS5 (A-Level)
Time Duration: 45 minutes
Class Size: 15 students
Curriculum Link:

• KS4 (GCSE AQA Computer Science - Programming Fundamentals)
  • "Understand and use arithmetic operators (+, -, *, /, %, //, **) in Python."
• KS5 (A-Level OCR Computer Science - Fundamentals of Programming)
  • "Use arithmetic operators to solve computational problems, demonstrating proficiency in procedural programming techniques."

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Lesson Objectives

By the end of this lesson, students will be able to:

1. Understand and demonstrate the use of arithmetic operators in Python.
2. Apply numeric data types and arithmetic operations correctly.
3. Solve real-world problems using arithmetic operations efficiently.
4. Debug simple arithmetic-related errors in Python scripts.

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Starter Activity (10 minutes)

Engage: The Shopping Challenge

• Display real-world receipts on the board (digital image or printed).
• Ask: “If a customer buys three items costing £4.50, £2.99, and £10.75, how would we calculate the total cost using Python?”
• Think-Pair-Share: Students brainstorm with a partner to write a one-line Python calculation on a mini-whiteboard.

Teacher’s Role:

• Observe responses and introduce Python's arithmetic symbols: +, -, *, /, //, %, **.

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Main Lesson (25 minutes)

Part 1: Exploring Python Arithmetic Operators (10 minutes)

Instructor Demonstration (Live Coding):

1. Write live code examples on a projector/screen:

   # Addition
   total = 5 + 3  
   print(total)  # Outputs 8
   
   # Subtraction  
   difference = 10 - 4  
   print(difference)  # Outputs 6
   
   # Multiplication  
   product = 7 * 2  
   print(product)  # Outputs 14
   
   # Division  
   quotient = 10 / 3  
   print(quotient)  # Outputs 3.333...
   
   # Floor Division  
   floor_result = 10 // 3  
   print(floor_result)  # Outputs 3
   
   # Modulus (Remainder)  
   remainder = 10 % 3  
   print(remainder)  # Outputs 1
   
   # Exponentiation  
   power = 2 ** 3  
   print(power)  # Outputs 8
   

2. Highlight how different operations might be used in real-world applications (e.g., currency calculations, stock inventory, scientific calculations).

Part 2: Hands-On Task – "Café Pricing System" (15 minutes)

Task Brief:

Students work in pairs to create a Python script for a café owner who wants a program to:

• Calculate the cost of buying multiple items.
• Apply a 10% discount if the total is over £20.
• Display the final amount with two decimal places.

Example Code Guide:

# Prices of products  
coffee_price = 2.50  
cake_price = 3.75  

# Quantity purchased  
coffee_qty = int(input("Enter number of coffees: "))  
cake_qty = int(input("Enter number of cakes: "))  

# Total cost calculation  
total = (coffee_price * coffee_qty) + (cake_price * cake_qty)  

# Apply a discount if total is above £20  
if total > 20:  
    total *= 0.9  # Apply 10% discount  

# Display result with two decimal places  
print(f"Final cost: £{total:.2f}")  

Challenge Extension:

• Introduce a service charge of 5% if the total is above £30.
• Allow for input validation, ensuring users only enter positive numbers.

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Plenary (10 minutes)

Debugging Challenge – "Spot the Error"

• Show students a faulty Python snippet:

  total = (10 * * 2) - (5 // 2)  
  printtotal  
  

  • Ask: "Can you find and fix the errors?"
  • Solution:

    total = (10 ** 2) - (5 // 2)  
    print(total)  # Outputs 98  
    

Class Discussion:

• What types of common errors can occur with arithmetic operations?
• How can indentation and syntax affect the output?

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Assessment & Homework

Formative Assessment (Recap Questions – 5 minutes)

1. What is the // operator used for?
2. What is the difference between / and %?
3. How can you raise a number to a power in Python?
4. What happens if you divide by zero in Python?

Homework Task – "Personal Budget Calculator"

• Write a Python program that:
  • Calculates weekly expenses based on user input (e.g., rent, groceries, travel).
  • Computes remaining money after expenses based on a given weekly budget.
  • Suggests how much the user can save if they want to set aside 20% of their remaining money.
  • Outputs the results in neat formatting.

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Differentiation & Inclusion

For High-Achievers:

• Add VAT (20%) to café pricing calculations before discounts.
• Provide real-world data sets and ask students to generate reports using arithmetic operations.

For SEN / EAL Students:

• Provide a glossary of key terms (integer, float, modulo, exponent).
• Use colour-coded syntax sheets to highlight function names vs. variables.
• Pair beginners with more advanced students for peer guidance.

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Resources & Materials

• Teacher computer + projector for live coding.
• Mini-whiteboards for brainstorming.
• Printed Python operator reference sheets.
• Python IDE installed on student computers (e.g., Thonny, IDLE, or VS Code).

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Reflection & Next Steps

• Teacher’s Self-Assessment: Were students comfortable with operator usage?
• Student Reflection: What was challenging about performing arithmetic in Python?
• Next Lesson Preview (Lesson 6/6):
  • Conditional Statements & Logical Operators – Using arithmetic operations within control structures (if and elif statements).

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Teacher's Note:
This lesson balances theory with practical application, embedding real-life problem-solving into Python arithmetic. Students will leave with a strong grasp of using operators and debugging basic errors.