PCEP Computer Programming and Python Fundamentals Practice Question
A junior developer writes a Python script to calculate the average of three numbers: avg = a + b + c / 3. What is the problem with this code?
⚠ Common exam trap
The PCEP exam often tests the misconception that Python evaluates expressions strictly left-to-right, leading candidates to think `a + b + c / 3` works correctly, when in fact operator precedence overrides left-to-right evaluation.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Missing parentheses cause incorrect order of operations
Python follows the standard mathematical order of operations (PEMDAS/BODMAS), where division has higher precedence than addition. The expression `a + b + c / 3` is evaluated as `a + b + (c / 3)`, which calculates the average incorrectly. To compute the correct average, parentheses must be used: `(a + b + c) / 3`.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Division by a variable is not allowed
Why it's wrong here
Python divides by variables freely; the divisor here is the literal 3, not a variable. Variable divisors are valid in any expression, and would be relevant only if the language restricted runtime division, which Python does not.
- ✓
Missing parentheses cause incorrect order of operations
Why this is correct
Division binds tighter than addition, so a + b + c / 3 computes a + b + (c/3), not (a+b+c)/3. Wrapping the sum in parentheses restores the intended grouping, satisfying the stem's requirement for a correct average calculation across all three numbers.
- ✗
Python cannot divide integers
Why it's wrong here
Python's / operator returns a float for integer operands, so integer division is permitted. True integer truncation occurs with //, and would be the issue only if the script required floor division semantics rather than a correct average.
- ✗
Variable names are too short
Why it's wrong here
Name length has no bearing on evaluation; Python binds any valid identifier. Short names are merely a readability concern, and would be the answer only if the question asked about style or maintainability rather than operator precedence.
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