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Hard Difficulty Questions

Practise CompTIA Data+ (DA0-002) practice questions — original exam-style scenarios covering every exam domain, with detailed explanations, wrong-answer analysis, and common exam traps.

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DA0-002
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CompTIA
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Scenario guide

How to approach hard difficulty questions

These are the questions most candidates get wrong. They require connecting multiple concepts, reading tricky output, or knowing edge-case behaviour that isn't on most study cards. Practising them trains you to operate under uncertainty — a necessary skill on the real exam.

Quick answer

Hard Difficulty Questions questions test whether you can apply the concept in context, not just recognise a definition.

How the topic appears in realistic exam-style scenarios.

Which detail in the question changes the correct answer.

How to eliminate plausible but wrong options.

How to connect the question back to the wider exam objective.

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Practice set

Practice scenarios

Question 1hardmultiple choice
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Refer to the exhibit. A data architect is designing a data dictionary for a relational database. Based on the exhibit, which data concept is being illustrated?

Exhibit

{
  "employee": {
    "emp_id": { "type": "integer", "nullable": false, "primary_key": true },
    "name": { "type": "string", "nullable": false },
    "email": { "type": "string", "nullable": true, "unique": true },
    "department": { "type": "string", "nullable": true }
  }
}
Question 2hardmultiple choice
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A data engineer is designing a system to store raw sensor data from thousands of IoT devices. The data will be used later for various analytics projects, but the schema is not yet defined. Which storage solution is most appropriate?

Question 3hardmultiple choice
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A data analyst includes a map showing customer locations by zip code. The map reveals exact addresses for a few customers due to data granularity. This violates which principle?

Question 4hardmultiple choice
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A data analyst is using a public API to collect historical weather data. The API has a rate limit of 100 requests per minute, but the analyst needs to retrieve 10,000 records as quickly as possible. What strategy should be used?

Question 5hardmultiple choice
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An analyst is fitting a polynomial regression model and wants to choose the degree that minimizes overfitting. Which technique should the analyst use?

Question 6hardmultiple choice
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In Tableau, you want to create a view showing the total sales per region, but also want to allow users to filter by year without losing the ability to see all regions. What feature should you use to compute the total sales that ignores the year filter?

Question 7hardmultiple choice
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A company is merging two databases from different departments. In Database A, customer IDs are integers. In Database B, customer IDs are alphanumeric strings. To merge, the data analyst must reconcile these differences. Which step should be taken first?

Question 8hardmultiple choice
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Given the linear regression output, which independent variable has the strongest effect on price, based on standardized coefficients?

Exhibit

Refer to the exhibit.

Call:
lm(formula = price ~ sqft_living + bedrooms + bathrooms, data = housing)

Residuals:
    Min      1Q  Median      3Q     Max
-1.2345 -0.3456 -0.0123  0.3456  2.3456

Coefficients:
              Estimate Std. Error t value Pr(>|t|)
(Intercept)   0.123456   0.012345  10.000  <2e-16 ***
sqft_living   0.001234   0.000123  10.000  <2e-16 ***
bedrooms     -0.056789   0.012345  -4.600  4.23e-06 ***
bathrooms     0.234567   0.045678   5.135  3.45e-07 ***
--
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.4567 on 496 degrees of freedom
Multiple R-squared:  0.789, Adjusted R-squared:  0.787
F-statistic: 617.8 on 3 and 496 DF,  p-value: < 2.2e-16
Question 9hardmulti select
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Which THREE are best practices for acquiring data via web scraping? (Select exactly 3)

Question 10hardmulti select
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Which THREE of the following are assumptions of linear regression? (Select THREE).

Question 11hardmultiple choice
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A data analyst is creating a self-service reporting environment. Which data governance practice ensures users see only data relevant to their department?

Question 12hardmultiple choice
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An analyst notices that a dashboard displays conflicting data from two sources. What is the first step in troubleshooting?

Question 13hardmultiple choice
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Based on the exhibit, what is the most likely cause of the import failure?

Exhibit

Refer to the exhibit.

Data Import Log:
[2024-03-15 10:22:34] INFO: Starting import from source 'sales_raw.csv'
[2024-03-15 10:22:35] WARN: Row 1502: 'price' field contains non-numeric value '12.5A'. Skipping row.
[2024-03-15 10:22:36] ERROR: Row 3450: 'date' field value '2024-02-30' is invalid. Import halted.
[2024-03-15 10:22:36] INFO: Import process terminated with errors.
Question 14hardmultiple choice
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A healthcare data analyst is presenting findings on patient readmission rates to a group of hospital administrators. The analysis reveals a 15% increase in readmissions over the past quarter for patients aged 65+ from a specific zip code. However, the administrators are skeptical because previous quarterly reports showed no such trend, and they suspect data quality issues. The analyst must communicate this insight effectively while maintaining credibility. Which of the following approaches should the analyst take?

Question 15hardmultiple choice
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A data analyst is performing a chi-square test of independence on a contingency table of customer satisfaction (satisfied vs. dissatisfied) and product type (A, B, C). The test yields a p-value of 0.04 with α = 0.05. What is the correct conclusion?

Question 16hardmultiple choice
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A data analyst runs an A/B test on a new website layout. The test yields a p-value of 0.04 with the null hypothesis being no difference in conversion rates. The significance threshold is α=0.05. Which of the following is the correct conclusion?

Question 17hardmulti select
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A company runs an A/B test to compare a new website layout (treatment) against the current layout (control). The conversion rate for the control is 5% and for the treatment is 5.5%. The p-value is 0.06 at α=0.05. Which THREE of the following conclusions are valid?

Question 18hardmultiple choice
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A research firm is acquiring data from public government databases via API. The API rate limits at 100 requests per minute. They need to download 10,000 records, but each request returns a maximum of 100 records. What is the most efficient approach to ensure complete acquisition without being blocked?

Question 19hardmulti select
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An e-commerce company wants to analyze sales performance across product categories. The dataset includes transaction amounts and a column 'category' with values (Electronics, Clothing, Home). The analyst decides to use stratified sampling to ensure proportional representation. Which THREE steps are required to implement this? (Select THREE).

Question 20hardmultiple choice
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A healthcare organization is building a data warehouse to support population health analytics. The data sources include: (1) an electronic health record (EHR) system with a relational database containing patient demographics, diagnoses, and medications; (2) a claims system that generates CSV files daily; (3) patient-generated health data from mobile apps via a REST API returning JSON. The data engineer needs to design a data acquisition process that runs nightly. The EHR system has a change tracking mechanism that logs changes with timestamps. The claims CSV files are appended daily. The API supports filtering by date. The data warehouse uses a star schema with fact and dimension tables. The engineer must ensure data consistency and minimize load times. Which approach should the engineer take?

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