041 | Correct: B
DNS: The Internet's Address Directory
DNS maps domain names to IP addresses. Encrypting communications and removing viruses are separate functions.
ROUND 5 RESULT
6 / 10
Accuracy: 60%
6 correct answers and 4 incorrect answers out of 10.
Correct answers covered DNS, email security, SQL, system availability, project management, and digital signatures. Areas for review include algorithms, SaaS, data leakage, and testing methods.
Note: An interim grading display incorrectly showed “5/10.” The official result based on the answer key is 6/10 (60%).
01 | Score Summary
| Question | Topic | Your Answer | Correct Answer | Result |
|---|---|---|---|---|
| 041 | DNS | B | B | Correct |
| 042 | Email Attachment Safety | A | A | Correct |
| 043 | SQL JOIN | C | C | Correct |
| 044 | Summing Integers Efficiently | B | D | Incorrect |
| 045 | Availability of a Series System | B | B | Correct |
| 046 | SaaS | D | C | Incorrect |
| 047 | Critical Path | A | A | Correct |
| 048 | AI Data Leakage | A | D | Incorrect |
| 049 | Digital Signatures | B | B | Correct |
| 050 | Black-Box Testing | B | C | Incorrect |
02 | Explanations for All 10 Questions
042 | Correct: A
Check the Sender and Contents Before Opening Attachments
The basic precaution is not to open suspicious attachments casually. Because emails can impersonate people you know, the displayed sender alone does not guarantee safety.
043 | Correct: C
JOIN Connects Tables
Use a shared customer ID to join the customer and order tables. ORDER BY sorts, GROUP BY groups records, and DELETE removes records.
044 | Your Answer: B → Correct: D
Find the Sum from 1 to 100 with a Formula
Instead of adding every number from 1 to 100 individually, pair the first and last numbers.
100 × 101 ÷ 2 ＝ 5,050
“Adding 100 one hundred times” gives 10,000, not the requested sum.Reducing the number of calculationsis a key idea in algorithm design.
045 | Correct: B
Multiply Availability Rates in a Series System
0.99 × 0.99 ＝ 0.9801 ＝ 98.01％
Because both devices must be operating for the system to work, multiply their independent availability probabilities.
046 | Your Answer: D → Correct: C
SaaS Means Using Ready-Made Software as a Service
SaaS lets users access business software and similar applications over the internet; it does not mean building a data center yourself. In simple terms, IaaS provides infrastructure such as virtual servers, PaaS provides development and runtime environments, and SaaS provides ready-to-use software.
047 | Correct: A
The Critical Path Determines the Project Timeline
A delay in an activity on the critical path delays the overall project completion. These activities deserve close progress monitoring.
048 | Your Answer: A → Correct: D
Data Leakage Means Including Information That Should Not Be Available
If future stock prices are included when training a model intended to predict the past, the model may appear unrealistically accurate. Load balancing (A), by contrast, distributes processing across multiple machines or resources.
Here, data leakage means unintended information entering machine-learning training or evaluation, not the external disclosure of personal information.
049 | Correct: B
Digital Signatures Help Verify Signers and Detect Tampering
Digital signatures help verify who signed data and whether the content has changed after signing. This differs from encryption used for confidentiality.
050 | Your Answer: B → Correct: C
Black-Box Testing Checks Behavior Without Looking Inside
Provide inputs and verify that the outputs match expectations. White-box testing examines internal processing structures, while static analysis examines code or related artifacts without executing the program.
03 | Strengths and Areas for Improvement
Strength | Understanding How Systems Work
You answered questions correctly when they involved relationships, such as multiplying availability rates, joining tables, and understanding schedule delays.
Area to Improve | Connecting Terms to Real Examples
Reviewing SaaS, data leakage, and black-box testing alongside concrete examples should help reinforce their definitions.
Area to Improve | Checking Calculations
For algorithm questions, make a habit of checking whether an answer choice actually produces the value requested.
04 | Connection to Yorimichi Research Laboratory
Question 048 Directly Relates to Stock-Market Backtesting
Suppose you recreate a trading decision as of 2024 but accidentally use information published in 2025. Your backtest may look better than it truly would have performed. That is the error of acting as though the future were already known.
What to Check:Timestamps of price data, publication dates of earnings information, the time range used to calculate features, and the separation of training and evaluation periods. These checks help make AI-based analysis more reliable.
05 | Learning Plan for Round 6
- Explain Terms in One Sentence:Describe SaaS, data leakage, and black-box testing in your own words.
- Check Calculations:For sums of sequences and similar problems, verify that the magnitude and meaning of your answer make sense.
- Connect Learning to Real Research:Check whether any future information has entered your backtesting process.
Next: Round 6 | Questions 051–060. We will revisit the four missed topics while also tackling unfamiliar questions.
Editorial note: This article records the questions, answers, and grading results from Round 5. It does not reproduce official past questions from Japan's Applied Information Technology Engineer Examination. This is a small 10-question learning experiment, not an estimate of the likelihood of passing the full examination.