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Grail, Inc. Interview Questions

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Machine Learning

RMS Error

Missing Housing Data

What are the logistic and softmax functions? What is the difference between the two?

Softmax vs Logistic

How to model merchant acquisition in a new market?

Merchant Acquisition

Random Forest Explanation

Data Structures & Algorithms

Moving Window

Given a json string with nested objects, write a function that flattens all the objects to a single key-value dictionary.

Flatten JSON

Write a function to impute the median price of the selected California cheeses in place of the missing values.

Impute Median

Weighted Keys

Given a list of strings, write a function that returns the longest common prefix

Common Prefix

Last Transaction

Given a users table, write a query to get the cumulative number of new users added by the day, with the total reset every month. 

Cumulative Reset

Cumulative Distribution

Write a SQL query to count transactions filtered by several criterias.

Count Transactions

Subscription Retention

Analytics

How would you analyze the dataset to understand exactly where the revenue loss is occurring?

Evaluating Revenue Decline

Describing a data project and its challenges

Hurdles In Data Projects

Strategically resolving misaligned expectations with stakeholders for a successful project outcome

Stakeholder Communication

How to present complex data insights with clarity and adaptability tailored to a specific audience

Presentations and Insights

Making data-driven insights actionable for those without technical expertise

Simple Explanations

Statistics

P-value to a Layman

Reducing Error Margin

Unbiased Estimator

Describe linear regression to various audiences with different levels of knowledge.

Explaining Linear Regression to Different Audiences

When an interviewer asks a question along the lines of:

<ul>
<li>What would your current manager say about you? What constructive criticisms might he give?</li>
<li>What are your three biggest strengths and weaknesses you have identified in yourself?</li>
</ul>

How would you respond?

When asked about your strengths in an interview, what is an effective way to respond?

When asked about your strengths in an interview, what is an effective way to respond?

Your Strengths and Weaknesses I

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Which of the following is an acceptable strategy when discussing weaknesses in an interview?

Your Strengths and Weaknesses II

What do you tell an interviewer when they ask you what your strengths and weaknesses are?

Your Strengths and Weaknesses

Brainteasers

When an interviewer asks you a question along the lines of:

<ul>
<li>Why did you apply to our company?</li>
<li>What are you looking for in your next job?</li>
<li>What makes you a good fit for our company?</li>
</ul>

How should you respond?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

When asked 'What are you looking for in your next job?' in an interview, how can you tie the company's employee benefits into your response?

Why Do You Want to Work With Us I

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

How can company values be used effectively in an interview when asked 'What makes you a good fit for our company?'

Why Do You Want to Work With Us II

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

When responding to the question 'Why did you apply to our company?' during an interview, what aspect should you highlight?

Why Do You Want to Work With Us III

How would you answer when an Interviewer asks why you applied to their company?

Why Do You Want to Work With Us

Describe a data project you worked on. What were some of the challenges you faced?

How would you explain what a p-value is to someone who is not technical?

What does a p-value in a statistical test represent?

What does a p-value in a statistical test represent?

P-value to a Layman I

In a statistical test, how does a low p-value (less than 0.05) influence our decision about the null hypothesis?

In a statistical test, how does a low p-value (less than 0.05) influence our decision about the null hypothesis?

P-value to a Layman II

Let’s say that you’re training a classification model.

How would you combat overfitting when building tree-based models?

Let's say that you're training a classification model.   How would you combat overfitting when building tree-based models?

Overfit Avoidance

How would you handle the data preparation for building a machine learning model using imbalanced data?

Addressing imbalanced data in machine learning through carefully prepared techniques.

Data Preparation for Imbalanced Data

Talk about a time when you had trouble communicating with stakeholders. How were you able to overcome it?

Given a string, write a function to determine if it is palindrome or not.

Note: A palindrome is a word/string that is read the same way forward as it is backward, e.g. <code>&#39;reviver&#39;</code>, <code>&#39;madam&#39;</code>, <code>&#39;deified&#39;</code> and <code>&#39;civic&#39;</code> are all palindromes, while <code>&#39;tree&#39;</code>, <code>&#39;music&#39;</code> and <code>&#39;person&#39;</code> are not palindromes.

Example:

Input:

<pre tabindex="0" class="chroma"><code>word1 = &#34;tree&#34;
word2 = &#34;radar&#34;
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>def is_palindrome(word1) -&gt; False
def is_palindrome(word2) -&gt; True
</code></pre>

Given a string, write a function to determine if it is palindrome or not.

String Palindromes

Explain the difference between the XGBoost and random forest algorithms and give an example where you would use one over the other.

Why might a data scientist choose to use XGBoost instead of Random Forest for a particular machine learning task?

Why might a data scientist choose to use XGBoost instead of Random Forest for a particular machine learning task?

XGBoost vs Random Forest: Choice

Xgboost vs Random Forest

How does random forest generate the forest? Additionally, why would we use it over other algorithms such as logistic regression?

What happens when you average the output on multiple decision trees?

What happens when you average the output on multiple decision trees?

Average Trees

Tell me about a project in which you had to clean and organize a large dataset.

Describing a real-world data cleaning and organization project

Data Cleaning Experiences

Data Pipelines

Let’s say we want to launch a re-design of a landing page to improve the click-through rate. We can do this by implementing an AB test.
Given that we launch an AB test, how would you infer if the results of the click-through rate were statistically significant or not?

How can you accurately conclude if the results of an A/B test, conducted to evaluate the effectiveness of a landing page redesign, are statistically significant?

How can you accurately conclude if the results of an A/B test, conducted to evaluate the effectiveness of a landing page redesign, are statistically significant?

Statistically Significant Test

Precisely ascertain whether the outcomes of an A/B test, executed to assess the impact of a landing page redesign, exhibit statistical significance.

A/B Testing

Regularization and cross-validation are two common techniques used to improve the performance of machine learning algorithms.

When should you use one versus the other?

Given the choices below, which one is an example of a scenario where we should be using regularization?

Given the choices below, which one is an example of a scenario where we should be using regularization?

Regularization Example

Regularization and Validation

How would you convey insights and the methods you use to a non-technical audience?

What’s the relationship between PCA and K-means clustering?

What does the variable “k” in k-means clustering refer to?

What does the variable "k" in k-means clustering refer to?

Input of K-means

PCA and K-Means

Describe a time when you had to define a long-term vision for a project or team and move it from concept to reality.

Interviews for leadership or senior technical roles look for more than just “finishing a project.” Your answer should specifically address:

<ol>
<li>The “Why”: What data or organizational gap necessitated this vision?</li>
<li>The Framework: How did you translate a high-level goal into a roadmap?</li>
<li>The Friction: How did you handle stakeholders or team members who were skeptical of the new direction?</li>
</ol>

Vision Setting and Execution Strategy

Business Case

We want to build a model to predict housing prices in the city of Seattle. We’ve scraped 100K sold listings over the past three years but found that around 20% of the listings are missing square footage data.

How do we deal with the missing data to construct our model?

We want to build a model to predict housing prices in the city of Seattle. We’ve scraped 100K sold listings over the past three years, but have discovered that around 20% of the listings are missing square footage data.

How would you approach dealing with this missing data, in order to construct the most useful predictive model possible?

We want to build a model to predict housing prices in the city of Seattle. We’ve scraped 100K sold listings over the past three years, but have discovered that around 20% of the listings are missing square footage data.

How would you approach dealing with this missing data, in order to construct the most useful predictive model possible?



Given two strings, write a function to return <code>True</code> if the strings are anagrams of each other and <code>False</code> if they are not.

Note: A word is not an anagram of itself.

Example 1:

Input:

<pre tabindex="0" class="chroma"><code>string_1 = &#34;listen&#34;
string_2 = &#34;silent&#34;
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>True
</code></pre>

Example 2:

Input:

<pre tabindex="0" class="chroma"><code>string_1 = &#34;banana&#34;
string_2 = &#34;bandana&#34;
</code></pre>

Output:

<pre tabindex="0" class="chroma"><code>False
</code></pre>

Valid Anagram

How would you explain the concept of linear regression to three different audiences: a child, a first-year college student, and a seasoned mathematician? Ensure your explanations are tailored to the understanding level of each audience.

An ecommerce company is experiencing a reduction in revenue for the past 12 months. You have the following transaction data:

<ul>
<li>Date of sale</li>

<li>Total $ Amount paid by customer</li>

<li>Profit Margin per unit</li>

<li>Quantity of item</li>

<li>Item category</li>

<li>Item subcategory</li>

<li>Marketing attribution source</li>

<li>% discount applied</li>
</ul>

How would you analyze the dataset to understand exactly where the revenue loss is occurring?

Let’s say you’re interning at a fintech startup that’s building a platform for online games of chance. During testing, one of your simulations flips a coin 10 times and gets 8 tails and 2 heads.

How would you determine if the coin is fair, and what statistical approach would you use to support your conclusion?

How would you assess if a coin is fair after observing 8 tails in 10 flips?

Fair Coin

Probability

How comfortable are you presenting your insights?

What are the logistic and softmax functions? What is the difference between the two?

What makes them useful for use in logistic regression?

In logistic regression, how is the predicted class determined based on the logistic function?

In logistic regression, how is the predicted class determined based on the logistic function?

Softmax vs Logistic II

What is the key characteristic of the logistic function that makes it useful for mapping continuous values to a probability?

What is the key characteristic of the logistic function that makes it useful for mapping continuous values to a probability?

Softmax vs Logistic I

Let’s say that you’re a data scientist at DoorDash.

How would you build a model to predict which merchants the company should go after for acquisition when entering a new market?

What are some effective ways to make data more accessible to non-technical people?

Demystifying data for non-technical users through visualization and clear communication

Accessible Data

Data Viz & Interpretation

What is an unbiased estimator and can you provide an example for a layman to understand?

What makes an estimator of a population statistic unbiased?

Let’s say your manager asks you to build a model with a neural network to solve a business problem.

How would you justify the complexity of building such a model and explain the predictions to non-technical stakeholders?

Which is the following domains is generally NOT a good use case for using a deep neural net?

Which is the following domains is generally NOT a good use case for using a deep neural net?

Neural Net Use Cases

Justify a Neural Network

Let’s say that you work for a company like Netflix. Netflix has two pricing plans: $15/month or $100/year.

Let’s say an executive at the company wants you to analyze the churn behavior of users that subscribe to either plan.

What kinds of metrics / graphs / models would you build to help give the executive an over-arching view of how the subscriptions are performing?

How would you present the performance of each subscription to an executive?

Analyzing Churn Behavior

Product Sense & Metrics

To improve customer experience on Uber Eats, what key parameters would you focus on improving?

Delivering an exceptional customer experience by focusing on key customer-centric parameters

Uber Eats Customer Experience

Write a function to get a sample from a standard normal distribution.

Write a function to get a sample from a standard normal distribution.

Normal Distribution Sample

Challenge

Grail, Inc. Salaries by Position

<h5>Staff Software Engineer For The Data Team </h5>GRAIL is seeking a Staff Software Engineer for the Data Team. This team designs, builds, and operates the software systems that manage GRAIL's end-to-end data lifecycle, from sample ingestion through downstream analysis, while meeting rigorous clinical, regulatory, and privacy standards. Our work directly supports clinical research, operations, and decision-making in the fight against cancer. In this role, you will take technical ownership of systems that produce trusted, analysis-ready datasets for use across GRAIL's research and clinical programs. This is a software engineering role focused on building complex production-grade systems that work with data in dynamic, regulated environments as opposed to assembling off-the-shelf ETL tools or writing SQL heavy pipelines. This position offers significant autonomy and scope for impact. You'll collaborate closely with research, clinical lab operations, and scientific teams, and lead efforts to improve how we structure, validate, and deliver critical scientific and clinical data. This is a hybrid role based in either Menlo Park, CA (moving to Sunnyvale, CA in Fall 2026) or Durham, NC. Our current hybrid policy requires on-site presence at least 60% of the time, including key in-person collaboration days. <h5>Responsibilities </h5><ul> <li>Design and implement software systems that turn raw clinical, lab, and operational data into reliable, analysis-ready datasets </li><li>Partner with scientists, clinicians, lab operations, and data teams to understand data generation, transformation, and usage needs </li><li>Develop services, libraries, data models, and workflow components that enforce data integrity, access control, and compliance by design </li><li>Navigate complex data requirements such as schema evolution, blinding, consent, and privacy compliance </li><li>Collaborate on cross-functional initiatives involving data quality, testing strategy, monitoring, and operational excellence </li><li>Lead software engineering efforts for long-lived systems that must evolve alongside active clinical and research programs </li><li>Mentor engineers and collaborate with scientists to ensure software decisions support both technical and scientific outcomes </li><li>Contribute to documentation, onboarding materials, and processes that support cross-functional adoption and data literacy across teams </li><li>Participate in incident response or investigation processes related to data quality or availability issues in production systems </li></ul> <h5>Required Qualifications </h5><ul> <li>7+ years of experience building production-grade software systems </li><li>Strong software engineering fundamentals, including system design, data modeling, API design, and writing well-tested production code. </li><li>Experience building and operating data-intensive software systems, not just declarative pipelines or SQL-only workflows </li><li>Proficiency in Go or Python (or similar general-purpose language) </li><li>Experience with data modeling, validation, and transforming real-world data into usable formats </li><li>BS in Computer Science, Engineering or Bioinformatics, or a related field, or equivalent practical experience </li></ul> <h5>Preferred Qualifications </h5><ul> <li>2+ years experience working in regulated or clinical data environments (e.g., HIPAA, CLIA, GCP, FDA compliance) </li><li>Direct experience working with or supporting scientific teams (e.g., bioinformatics, wet lab, clinical research) </li><li>Experience designing systems that manage laboratory or bioinformatics data (e.g., LIMS, sequencing pipelines, assay metadata) </li><li>Familiarity with GxP practices and regulatory reporting requirements in clinical studies is a plus </li><li>Prior experience working in biotech, diagnostics, or life sciences companies </li><li>Experience supporting sample tracking, structured scientific data pipelines, or cross-functional data lifecycle management </li><li>Experience designing systems with data sequestration, permissioning, or privacy controls </li><li>Experience writing or contributing to software libraries, shared tooling, or reusable components used by other teams </li><li>Advanced degree (MS or PhD) in computer science, engineering, bioinformatics or a related discipline </li></ul> Expected full time annual base pay scale for the bay area is $163K-$216K. Actual base pay will consider skills, experience and location. This role may be eligible for other forms of compensation, including an annual bonus and/or incentives, subject to the terms of the applicable plans and Company discretion. This range reflects a good-faith estimate of the range that the Company reasonably expects to pay for the position upon hire; the actual compensation offered may vary depending on factors such as the candidate's qualifications. Employees in this role are also eligible for GRAIL's comprehensive and competitive benefits package, offered in accordance with our applicable plans and policies. This package currently includes flexible time-off or vacation; a 401(k) retirement plan with employer match; medical, dental, and vision coverage; and carefully selected mindfulness programs. GRAIL is an equal employment opportunity employer, and we are committed to building a workplace where every individual can thrive, contribute, and grow. All qualified applicants will receive consideration for employment without regard to race, color, religion, national origin, sex, gender, gender identity, sexual orientation, age, disability, status as a protected veteran, or any other class or characteristic protected by applicable federal, state, and local laws. Additionally, GRAIL will consider for employment qualified applicants with arrest and conviction records in a manner consistent with applicable law and provide reasonable accommodations to qualified individuals with disabilities.

Calculate Moving Average	SQL	Easy
Predict Customer Churn	Machine Learning	Medium
A/B Test Significance	Statistics	Medium
Optimize Query Performance	SQL	Hard
Feature Importance Analysis	Machine Learning	Medium
Clean Missing Data	Python	Easy
Neural Network Architecture	Deep Learning	Hard
Calculate Cohort Retention	SQL	Medium
Bayesian Probability	Statistics	Easy
Recommend Similar Products	Machine Learning	Hard

Grail, Inc. Interview Questions

Grail, Inc. Interview Guides