Consider a collection named students with the following documents: What is the query to retrieve the average score for each subject across all students in the students collection?

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Guide for C100DEV: MongoDB Certified Developer Associate

Quiz C100DEV: MongoDB Certified Developer Associate

Updated on 2026/09/07

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Guide for C100DEV: MongoDB Certified Developer Associate

Updated on 2026/09/07

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Quiz

Question 1/101/10

Consider a collection named students with the following documents:
Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 1-764603282

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 1-764603282

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 2-2398574842

What is the query to retrieve the average score for each subject across all students in the
students collection?

Select the answer:Select the answer

1 correct answer

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 3-676368871

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 4-1266336477

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 5-214350824

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 6-3432481124

Correct answer:
1. db.students.aggregate([
2. {
3. $unwind: "$scores"
4. },
5. {
6. $group: {
7. _id: "$scores.subject",
8. average_score: { $avg: "$scores.score" }
9. }
10. }
11. ])
Here's a breakdown of this query:
1. $unwind: "$scores": This stage is used to deconstruct the scores array field, creating
separate documents for each element within the array. This allows us to perform
calculations on individual scores.
2. $group: This stage groups the documents based on the _id field, which is set
to "$scores.subject". It groups the documents by the subject and allows us to perform
aggregate operations on each group.
3. average_score: { $avg: "$scores.score" }: Within the $group stage, we use
the $avg aggregation operator to calculate the average score for each subject.
The "$scores.score" represents the score value within the scores array.
Incorrect answers:
1. db.students.aggregate([
2. {
3. $group: {
4. _id: "$scores.subject",
5. average_score: { $avg: "$scores.score" }
6. }
7. }
8. ])
It doesn't consider the fact that the scores are stored as an array within each document.
Without unwinding the scores array, the $avg operator would operate on the entire array,
resulting in an incorrect average score for each subject.
1. db.students.aggregate([
2. {
3. $push: "$scores"
4. },
5. {
6. $group: {
7. _id: "$scores.subject",
8. average_score: { $avg: "$scores.score" }
9. }
10. }
11. ])
It uses the $push operator on the scores field. The $push operator is used to add values to an
array field, but in this case, it would create an array of arrays ([[scores1, scores2, ...]]),
which is not what we want. It would not allow us to calculate the average score correctly.
1. db.students.aggregate([
2. {
3. $unwind: "$scores"
4. },
5. {
6. $group: {
7. _id: "$subject",
8. average_score: { $avg: "$score" }
9. }
10. }
11. ])
It references the fields "$subject" and "$score" in the $group stage without considering the
fact that they are nested within the scores subdocuments. The correct references should
be "$scores.subject" and "$scores.score". Therefore, this query would not provide accurate
results for calculating the average scores.
https://www.mongodb.com/docs/manual/reference/operator/aggregation/group/

Right Answer: B

Quiz

Question 2/102/10

Which cursor method should you use to get information about the query plan?

Select the answer:Select the answer

1 correct answer

cursor.map()

cursor.size()

cursor.hint()

cursor.explain()

Quiz

Question 3/103/10

Which of the following statements correctly describes the relationship between BSON and JSON in
MongoDB?

Select the answer:Select the answer

1 correct answer

BSON and JSON are exactly the same data format, and the terms can be used interchangeably.

MongoDB uses JSON for data storage, and BSON is only used for querying data.

BSON is a binary representation of JSON-like documents, with additional data types not found in JSON.

BSON is a subset of JSON and only includes a portion of JSON's data types.

Quiz

Question 4/104/10

Which cursor method should you use to specify the maximum number of documents
returned?

Select the answer:Select the answer

1 correct answer

cursor.limit()

cursor.hint()

cursor.skip()

cursor.map()

cursor.count()

Quiz

Question 5/105/10

What is a MongoDB driver?

Select the answer:Select the answer

1 correct answer

A software that allows communication between an application and a MongoDB database.

A graphical user interface (GUI) for interacting with MongoDB databases.

A feature that ensures data integrity in MongoDB.

A database query language specific to MongoDB.

Quiz

Question 6/106/10

Which of the following rules (when ordering) should be followed when building query indexes?

Select the answer:Select the answer

1 correct answer

equality, sort, range

equality, range, sort

There is no specific rule.

range, sort, equality

Quiz

Question 7/107/10

Assume you have a MongoDB collection users with the following document structure:
Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 7-151029024

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 7-151029024

You are asked to perform an operation that inserts a new order into the "orders" array for the user
with a specific _id. Which of the following options will correctly accomplish this task?

Select the answer:Select the answer

1 correct answer

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 8-4096482644

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 9-3551216077

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 10-115181016

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 11-541322076

Quiz

Question 8/108/10

Which of the following statements correctly describes how an application connects to MongoDB using a
driver?

Select the answer:Select the answer

1 correct answer

The application connects to MongoDB through a message queue system, where messages containing database operations are exchanged.

The application connects to MongoDB by embedding JavaScript code within HTML pages and executing queries using a web browser.

The application connects to MongoDB using a driver that encapsulates the communication protocol and handles the interaction with the database server.

The application connects to MongoDB using a RESTful API to send HTTP requests and receive responses.

Quiz

Question 9/109/10

Which of the following queries can use an index on the "title" field? Select all correct answers.

Select multiple answer: (Choose 2)Select the answer

2 correct answers

db.movies.find( { "_id": 245 } )

db.movies.find( { "genres": "Drama", "type": "series" } )

db.movies.find()

db.movies.find( { "title": "Death Note" } )

db.movies.find( { "title": "Titanic" } )

Quiz

Question 10/1010/10

Suppose you have a developers collection with the following document structure:

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 12-621608654

Certification Exam C100DEV: MongoDB Certified Developer Associate MongoDB MongoDB-C100DEV 12-621608654

Select the query that can be executed without errors.

Select the answer:Select the answer

1 correct answer

db.developers.updateOne( { _id: 1 }, { $unset: { _id: '' } } )

db.developers.updateOne( { _id: 1 }, { $set: { fname: 'John' } } )

db.developers.updateOne( { _id: 1 }, { $set: { _id: 3, fname: 'Bob' } } )

db.developers.updateOne( { _id: 1 }, { $set: { _id: 3 } } )

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Quiz name:C100DEV: MongoDB Certified Developer Associate
Total number of questions:296
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