Quick Answer
The answer is to cast `sum` to `double` before division, changing `sum / numbers.length` to `(double) sum / numbers.length`. This fix is necessary because the original code performs integer division in the average method: both `sum` and `numbers.length` are integers, so Java truncates the fractional part, yielding a whole number instead of a precise double. For the array {10, 20, 30}, the correct average is 20.0, and while integer division coincidentally returns 20, the error becomes obvious with values like {10, 20, 31}, where the true average 20.333... would be incorrectly truncated to 20. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of type promotion and the common trap of forgetting that dividing two integers always produces an integer result, even when assigned to a double. A reliable memory tip: when computing averages, always cast one operand to double first—think "double before divide" to preserve the decimal.
This 1Z0-811 practice question tests your understanding of arrays and methods. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A method 'public static double average(int[] numbers) { int sum = 0; for (int i = 0; i < numbers.length; i++) sum += numbers[i]; return sum / numbers.length; }' is called with array {10, 20, 30}. What change is needed to return the correct average?
Change the loop to for (int i = 1; i <= numbers.length; i++)
Why wrong: Loop index is off-by-one and does not solve division issue.
Change 'sum / numbers.length' to '(double) sum / numbers.length'
Ensures floating-point division.
Change return type to int
Why wrong: Still integer division, and average may be fractional.
Add a second parameter for the length
Why wrong: Unnecessary and changes signature.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Change 'sum / numbers.length' to '(double) sum / numbers.length'
The method performs integer division because both `sum` (int) and `numbers.length` (int) are integers, truncating the fractional part. Casting `sum` to `double` before division forces floating-point arithmetic, preserving the decimal value. For the array {10, 20, 30}, the correct average is 20.0, but integer division yields 20 (truncated from 20.0, though here it matches by coincidence; for non-integer averages like {10, 20, 31}, the error would be obvious).
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Change the loop to for (int i = 1; i <= numbers.length; i++)
Why it's wrong here
Loop index is off-by-one and does not solve division issue.
Change 'sum / numbers.length' to '(double) sum / numbers.length'
Why this is correct
Ensures floating-point division.
Related concept
Read the scenario before looking for a memorised answer.
Change return type to int
Why it's wrong here
Still integer division, and average may be fractional.
Add a second parameter for the length
Why it's wrong here
Unnecessary and changes signature.
Common exam traps
Oracle often tests the distinction between integer and floating-point division in Java, trapping candidates who overlook that dividing two ints always truncates the decimal, even when assigned to a double variable or returned from a double method.
Detailed technical explanation
In Java, binary numeric promotion occurs for arithmetic operators: if both operands are integers, the result is an integer type (int, long, etc.). Casting one operand to `double` triggers widening primitive conversion, promoting the other operand to `double` as well, yielding a `double` result. This is a common pitfall in data analysis or scientific computing where precision matters, such as calculating mean temperatures or sensor readings.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 1Z0-811 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Arrays and Methods — This question tests Arrays and Methods — Read the scenario before looking for a memorised answer..
The correct answer is: Change 'sum / numbers.length' to '(double) sum / numbers.length' — The method performs integer division because both `sum` (int) and `numbers.length` (int) are integers, truncating the fractional part. Casting `sum` to `double` before division forces floating-point arithmetic, preserving the decimal value. For the array {10, 20, 30}, the correct average is 20.0, but integer division yields 20 (truncated from 20.0, though here it matches by coincidence; for non-integer averages like {10, 20, 31}, the error would be obvious).
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
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