Basic 30 Machine Learning Interview Questions & Answers

Machine Learning Interview Questions
Basic 30 Machine Learning Interview Questions & Answers

Machine Learning is a fast-expanding discipline in technology and data science. As organizations increasingly leverage the power of data, machine learning algorithms, and models play a crucial role in extracting valuable insights and making data-driven decisions. In this article, we will explore 30 basic machine-learning interview questions and provide comprehensive answers to help you prepare for your machine-learning job interviews.

What is Machine Learning?

Machine Learning is a subfield of artificial intelligence that focuses on creating algorithms and models that can learn from data and make predictions or take actions without being explicitly programmed. It enables computers to learn and improve from experience, automatically adapting to changing environments.

30 basic machine-learning interview questions with comprehensive answers

There are some important questions that are commonly asked during a machine learning interview, and they often revolve around a set of 30 basic machine learning interview questions with comprehensive answers:

1. What Are the basic types of Machine Learning?

Supervised Learning: Supervised learning involves training a model using labeled data, where the input and the corresponding output are known. The model learns to map inputs to outputs and can make predictions on new, unseen data.

Unsupervised Learning: Unsupervised learning deals with unlabeled data, where the model learns to identify patterns, relationships, and structures within the data without any predefined labels or outputs.

Reinforcement Learning: Reinforcement learning focuses on training an agent to make a sequence of decisions in an environment to maximize a reward signal. The agent learns through trial and error, receiving feedback from the environment.

2. What is Overfitting, and How Can You Avoid It?

Overfitting happens when a machine learning model grows too complicated and performs well on training data but fails to generalize to new, previously unknown data. To avoid overfitting, techniques like cross-validation, regularization, and early stopping can be employed. These methods help in balancing the model’s complexity and generalization ability.

3. What are a Machine Learning Model’s ‘Training Set’ and ‘Test Set’?

In a machine learning model, the training set is the data used to train the model, while the test set is a separate dataset used to evaluate the model’s performance. The training set helps the model learn patterns and relationships, while the test set provides an unbiased assessment of the model’s performance on new data. The allocation of data among training, validation, and test sets depends on the dataset size, but commonly used splits are 70-80% for training, 10-15% for validation, and 10-15% for testing.

It is important to allocate enough data for training to ensure the model learns effectively, while the validation set helps in tuning hyperparameters and preventing overfitting. The test set serves as an unbiased evaluation to assess the model’s performance.

4. How Should Missing or Corrupted Data in a Dataset Be Handled?

Missing or corrupted data can adversely affect the performance of machine learning models. Common approaches to handle such data include:

  • Removing instances or features with a high percentage of missing values.
  • Imputing missing values with statistical measures like mean, median, or mode.
  • Using sophisticated imputation techniques such as regression or multiple imputation.
  • Applying algorithms that can handle missing data directly, such as decision trees or random forests.

5. How Do You Select a Classifier Based on the Size of the Training Set Data?

The choice of a classifier depends on various factors, including the size of the training set. Generally, with a small training set, it is advisable to use simpler models with fewer parameters to avoid overfitting. As the training set size increases, more complex models can be considered. However, it is essential to balance model complexity and interpretability with the available data size and complexity of the problem at hand.

6. Describe the Confusion Matrix in Relation to Machine Learning Algorithms

A confusion matrix is a performance evaluation tool used in machine learning to visualize and analyze the performance of a classification model. It is a table that compares the predicted labels with the actual labels in a dataset. The matrix contains four values: true positives (TP), true negatives (TN), false positives (FP), and false negatives (FN). From these values, various performance metrics such as accuracy, precision, recall, and F1 score can be calculated.

7. What Are False Positives and False Negatives, and Why Are They Important?

In a binary classification problem, a false positive occurs when the model predicts the positive class incorrectly, while a false negative occurs when the model predicts the negative class incorrectly. False positives and false negatives have different significance depending on the problem context. For example, in a medical diagnosis scenario, a false positive means wrongly classifying a healthy person as diseased, while a false negative means failing to detect a disease in an affected person. The significance of false positives and false negatives varies based on the consequences of the classification error.

8. What Are the Three Stages of Model Development in Machine Learning?

The three stages of building a model in machine learning are:

  • Data Preprocessing: Involves data cleaning, handling missing values, transforming features, and normalizing data.
  • Model Training: Involves selecting an appropriate algorithm, training the model on the training data, and tuning hyperparameters.
  • Model Evaluation and Testing: This involves evaluating the model’s performance on validation and test sets, assessing metrics, and fine-tuning the model if necessary.

9. What is Deep Learning?

Deep Learning is a subject of machine learning that focuses on learning representations and patterns from complicated data using artificial neural networks with several layers. Deep learning models, also known as deep neural networks, can extract hierarchical features from raw data automatically, allowing them to tackle complicated tasks such as image identification, natural language processing, and audio recognition.

10. Differences Between Deep Learning and Machine Learning?

Machine learning Deep learning
Machine Learning is a broader field that encompasses various algorithms and techniques to enable computers to learn from data and make predictions.
Machine Learning often requires explicit feature engineering, where domain knowledge is used to extract relevant features.
Deep Learning is a specific subfield of machine learning that uses deep neural networks with multiple layers.
Deep Learning models can handle large-scale, unstructured data efficiently, while traditional machine learning models may struggle with such data.

11. What Are the Uses of Supervised Machine Learning in Today’s Businesses?

Supervised machine learning has numerous applications in modern businesses, including:

  • Customer churn prediction
  • Fraud detection
  • Sentiment analysis
  • Recommendation systems
  • Image and speech recognition
  • Credit risk assessment
  • Demand forecasting
  • Medical diagnosis

12. What is Semi-supervised Machine Learning?

Semi-supervised machine learning is a hybrid technique of training that uses both labeled and unlabeled data. It leverages the small amount of labeled data along with a larger pool of unlabeled data to improve model performance. The unlabeled data assists in capturing the underlying structure and patterns, while the labeled data guides the learning process.

13. What Are Unsupervised Machine Learning Techniques?

Unsupervised machine learning techniques focus on extracting patterns and relationships from unlabeled data. Two common unsupervised techniques are:

  • Clustering: Clustering algorithms group similar instances together based on their features or distances.
  • Association: Association techniques discover relationships between items in a dataset, such as market basket analysis.

14. How Do Supervised and Unsupervised Machine Learning Differ?

Supervised learning uses labeled data to train models and make predictions based on known outputs. Unsupervised learning works with unlabeled data and aims to identify patterns and structures in the data without predefined outputs.

Supervised learning deals with prediction and classification tasks. Unsupervised learning focuses on tasks like clustering, anomaly detection, and dimensionality reduction.

15. What Is the Distinction Between Inductive and Deductive Machine Learning?

Inductive Machine Learning:

Inductive learning involves inferring general rules or patterns from specific instances or examples. It generalizes from observed examples to make predictions or classifications on unseen data.

Deductive Machine Learning:

Deductive learning starts with general rules or principles and uses them to make predictions or classifications based on specific instances. It applies existing knowledge to specific cases.

16. Compare K-means and KNN Algorithms.


K-means is an unsupervised clustering algorithm that aims to partition a dataset into K distinct clusters. It allocates data points to clusters repeatedly depending on their closeness to cluster centroids.

KNN (K-Nearest Neighbors):

KNN is a supervised classification algorithm that assigns a class label to a data point based on the majority class of its K nearest neighbors. It calculates the distance between data points to determine similarity.

Note: This question is very important for machine learning interview questions.

17. What Is ‘Naive’ in the Naive Bayes Classifier?

The term ‘naive’ in the Naive Bayes classifier refers to the assumption of feature independence. It assumes that the presence or absence of a particular feature is independent of the presence or absence of other features, which simplifies the probability calculations. Despite this simplifying assumption, Naive Bayes classifiers often perform well in practice.

18. Explain how Reinforcement Learning may be used to teach a system to play chess.

In a game of chess, a system can play using reinforcement learning by treating each move as a state and learning to maximize a reward signal, which could be winning or achieving a favorable outcome. The system learns through trial and error, adjusting its move selection based on feedback from the game environment, and optimizing its policy to make better moves over time.

19. How Will You Know Which Machine Learning Algorithm to Choose for Your Classification Problem?

Choosing the right machine learning algorithm for a classification problem depends on various factors, including the dataset size, complexity, linearity, interpretability requirements, and available computational resources. It often involves experimentation and comparison of different algorithms such as logistic regression, decision trees, random forests, support vector machines (SVM), or neural networks to identify the one that performs best on the given problem.

20. How is Amazon Able to Recommend Other Things to Buy? How Does the Recommendation Engine Work?

Amazon uses a recommendation engine that leverages machine learning algorithms and techniques. It analyzes historical user data, such as past purchases, browsing history, and ratings, to create user profiles and identify patterns. Based on these patterns, the recommendation engine suggests relevant products to users by comparing their profiles with other similar users or products.

21. When Will You Use Classification over Regression?

Classification is used when the task involves predicting discrete class labels or categorical variables. It is suitable for problems like email spam detection (classifying emails as spam or not), sentiment analysis (classifying sentiments as positive, negative, or neutral), or disease diagnosis (classifying patients as diseased or healthy). Regression, on the other hand, is used when the task involves predicting continuous numerical values.

22. How Do You Design an Email Spam Filter?

Designing an email spam filter involves several steps:

  • Preprocessing: Cleaning and preparing email data, removing stop words, and transforming text into numerical representations.
  • Feature Extraction: Extracting relevant features such as sender, subject, content, and attachments.
  • Model Selection: Choosing a suitable classification algorithm such as Naive Bayes, Support Vector Machines (SVM), or Random Forests.
  • Training: Training the selected model on labeled data, consisting of spam and non-spam emails.
  • Evaluation: Evaluating the model’s performance using metrics like accuracy, precision, recall, and F1 score.
  • Deployment: Deploying the spam filter into the email system for real-time filtering.

23. What is a Random Forest?

Random Forest is an ensemble learning system that predicts the future by mixing many decision trees. It generates a forest of decision trees, each of which is trained on a distinct subset of the data using random feature selection. To get the final forecast, the projections from individual trees are aggregated by voting or averaging.

Note: This question is very important for machine learning interview questions.

24. What is the difference between bias and variation?

In machine learning, the bias-variance trade-off reflects a balancing act. Increasing a model’s complexity reduces bias but increases variance, whereas decreasing model complexity raises bias but decreases variation. The objective is to discover an ideal point that minimizes both bias and variance, producing a model that generalizes effectively to previously unknown data.

25. Define Precision and Recall.


Precision is the fraction of accurately anticipated positive cases out of all positive instances forecasted. It is concerned with the accuracy of optimistic forecasts.


Recall measures the proportion of correctly predicted positive instances out of all actual positive instances. It focuses on the ability to identify positive instances correctly.

26. What is a Decision Tree Classification?

Decision tree classification is a supervised machine-learning approach that makes choices using a tree-like structure. It divides the input space into features and builds decision nodes to divide the data. Each leaf node represents a class label or a prediction, and each decision node represents a test condition.

27. What Is Decision Tree Pruning and How Is It Carried Out?

Pruning is a method of shrinking a decision tree by removing superfluous branches or nodes. It prevents overfitting and increases the generalization ability of the tree. Pre-pruning (stopping the tree’s growth early) or post-pruning (removing nodes after the tree has fully grown) can be done depending on particular criteria such as error rate or impurity metrics.

28. Briefly Explain Logistic Regression.

A prominent classification approach that models the connection between a set of independent factors and a binary dependent variable is logistic regression. By applying a logistic function (sigmoid) to a linear combination of the input characteristics, it predicts the likelihood of an instance belonging to a given class. It’s popular for binary classification problems.

29. What is Kernel SVM?

Kernel Support Vector Machines (SVM) is a non-linear decision boundary expansion to the basic SVM technique. It accomplishes this by mapping the data into a higher-dimensional feature space where linear separation is achievable using a kernel function. Kernel SVM is useful for dealing with complicated datasets when linear separation is not possible.

30. What Are Some Methods of Reducing Dimensionality?

Some methods for reducing dimensionality in machine learning include:

  • Principal Component Analysis (PCA)
  • Linear Discriminant Analysis (LDA)
  • t-SNE (t-Distributed Stochastic Neighbor Embedding)
  • Feature selection techniques like Forward Selection, Backward Elimination, or Recursive Feature Elimination (RFE)
  • Regularisation methods such as L1 and L2 regularisation


Machine learning interviews frequently cover a broad variety of subjects and questions. Being well-prepared with answers to typical queries, comprehending key principles, and having hands-on experience with various machine learning algorithms can increase your chances of success significantly.

Remember, these answers can serve as a starting point, but it’s essential to personalize and elaborate on them based on your understanding and expertise. Good luck with your machine-learning interviews!

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