PCEP Practice Question: Data Types, Variables, Basic I/O and Operators
A developer needs to check if a variable x is between 10 and 20 (inclusive). Which expression is correct?
⚠ Common exam trap
Watch out — candidates often confuse inclusive vs. exclusive boundaries and select Option A with strict inequalities, or they misunderstand that `or` (Option D) creates a condition that is always true, failing to recognize the need for `and` logic.
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
✓
10 <= x <= 20
Python supports chained comparison operators, allowing `10 <= x <= 20` to evaluate whether `x` is between 10 and 20 inclusive. This expression is equivalent to `(10 <= x) and (x <= 20)`, which checks both boundaries simultaneously.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
x > 10 and x < 20
Why it's wrong here
Using `>` and `<` excludes the boundary values, so x = 10 and x = 20 both evaluate to False, contradicting the inclusive requirement. The tempting aspect is that chained comparisons like this are idiomatic Python for open ranges, and would be the right choice if the question asked for values strictly between 10 and 20.
- ✗
x < 10 and x < 20
Why it's wrong here
Testing x < 10 and x < 20 requires both comparisons to hold, so any value below 10 satisfies it while 15 fails — the opposite of the intended range. Chained comparisons like 10 <= x <= 20 express a bounded interval. This pattern suits filtering values beneath a single threshold, not checking membership within two limits.
- ✓
10 <= x <= 20
Why this is correct
Python supports chained comparison operators, so 10 <= x <= 20 evaluates as (10 <= x) and (x <= 20). Both bounds are inclusive because <= is used, satisfying the stem's requirement to include 10 and 20 themselves. This is the idiomatic single expression for range checking.
- ✗
x >= 10 or x <= 20
Why it's wrong here
Using `or` makes the expression true for every number, since any value satisfies at least one comparison — x = 5 passes via `x <= 20`. The `and` operator is required so both bounds apply. `or` is correct when testing membership in separate ranges, such as x < 10 or x > 20.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCEP practice question is part of Courseiva's free Python Institute certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCEP exam.