Arithmetic and Assignment

Scenario: The cashier must calculate a subtotal and apply a discount.

New words, in plain English

• Operator - a symbol that performs an operation
• Operand - a value an operator works on
• Precedence - the order in which operations happen

Python supports + - / // % *. Parentheses make intent explicit. Short assignment forms such as count += 1 update an existing name.

Analogy: A Python program is like a clear set of instructions for a careful helper: names label things, indentation groups steps, and errors explain where the helper became confused.

A small, real example

subtotal = 6.50 * 3
discount = subtotal * 0.10
total = subtotal - discount
print(round(total, 2))

Tip: Money needs decimal-aware design in serious systems; floats are fine for learning but can contain tiny rounding errors.

Goal: Practice this idea in the py-variables-types challenge at /labs/python. Fix the broken program, run it yourself, then use check to prove the real end state.