Quant Trader Intern Interview Guide for Beginners — Pt.4 Technical Phone Screen

5 min readNov 28, 2018

We’re entering the home stretch! A lot of the advice here will overlap with the onsite for technical knowledge. In general, this is where companies diverge in their interview process and can have wildly different questions.

Here’s a quick overview of the topics: Mental Math, Probability, EV, and Brainteasers.

Looking for the other posts?

Pt.1: Background (Interview Prep and Organization)

Pt.2: Round 1 (Mental Math and Pattern Recognition)

Pt.3: Round 2 (HR Screens)

Pt. 5: Final Round

1. Effective Practice

Preparing for this interview will probably be the most time intensive portion of preparing for quant interviews. As such, let’s take some time to talk about how to use your time the most efficiently.

“I never practice, I only perform.” — Chance the Rapper

It’s conventional wisdom for any athlete, musician, or rapper that the way you practice is going to be the way that you’re going to perform. So that means, the best way to be ready to interview is to simulate interviewing environments as much as possible.

So, this means find the place that you will be doing your interviews and practice there. Turn off the music, keep out the distractions, and try to simulate how an hour long interview would go. Bonus points if you are able to get someone to stand in as your interviewer.

Finally, take notes on how a day’s performance was. Which problems did you find challenging? What exterior factors may have caused your performance today to be especially good / bad. Which concepts do you need to focus on next? Introspection is the key to improvement.

As you move through the interviews, write down the questions, work on any problem that you may have struggled with. These questions will help guide you through the onsite, giving you a feeling about what types of questions each firm favors.

Aside: How many piano tuners live in Chicago? How many golf balls fit in the sun? These are examples of questions that have for the most part gone out of style. The second question, a Fermi question used to be the bee’s knees, but except for Akuna Capital, I did not see a single instance of these questions. They’re a fun exercise to think about, but if you are purely looking to become interview ready, your time would be most effective studying other material. If you have extra time, here is a good site detailing how to prepare. http://www.physics.uwo.ca/science_olympics/events/puzzles/fermi_questions.html

2. Mental Math (Advanced)

I hope that you’ve kept your mental math skills up to snuff since the first round. If you need some help getting back to snuff, go back through the mental math portion in my article about round 1.

The major differences between now and the first round are: the fact that all questions and answers will be spoken and a much higher focus on estimation and confidence intervals.

For most people, being able to do mental math by talking to people should not be any harder than doing it on the computer. As a visual learner, this was not the case for me. Take the time to make sure that you won’t have any troubles with this transition by getting a friend to read out loud to you zetamac questions.

With the basics squared away, it’s time to focus on square roots. I have no idea why, but the field of quant finance has an obsession with square roots, with over half of the companies I interviewed at incorporating them in some way. I recommend reading through all the answers in this quora post and figure out which strategy works the best for you.

Mental Math: How does my friend calculate the square root of any number so accurately?

In my former life as a teacher, I would calculate square roots in my head while invigilating exams, and there were two…

www.quora.com

With your method, start practicing square roots. Do large numbers >10,000, decimals, and everything in between. In addition, practice giving 90% confidence intervals (an interval in which you are 90% sure the real value lies between).

3. Probability

XKCD about Bayes, if you don’t find this funny, study until you do.

Probability is a wily beast where you probably will spend most of your time. For the most part, probability can be split into a couple subtopics (listed in decreasing importance): Conditional, EV, and game theory.

Luckily, this topic gets covered extremely well by A Practical Guide to Quantitative Finance Interviews. For the most part, internships will have a slightly reduced problem space, as such, do only chapters: 4.1, 4.2, 4.3, 4.5, and 5.1.

Aside: This skips topics on distributions which have been brought up during interviews, but I received no demerits by simply saying that I never studied anything about them. In some cases, they would still ask questions regarding distributions, but they would present the question with enough information such that no background knowledge was required.

After finishing this section, you should be able to do most of the questions in Mark Joshi’s Quant Job Interview Questions and Answers.

Further questions to consider would be expected value of the number of coin tosses to get 3 H in a row. Expected value of the max of two dice thrown at the same time. In general, you should have a sense of how good you are at these questions. Scour Glassdoor and the internet doing practice problems until you feel 100%.

4. Brainteasers

Brainteasers have generally fallen out of vogue. However, I do believe that they should still be studied, since some probability questions that will be asked will involve aspects of brainteasers that will help you come to the correct answer. Quite simply, just do all of chapter 3 of A Practical Guide to Quantitative Finance Interviews.

These are tough and really cannot be studied too well. So, godspeed fellow traveller.

5. Conclusion

This will be the most difficult part of the process, since preparing for this will likely make you amply prepared for the onsite interviews. Remember to do effective practice and to write down the questions you receive from the various companies you interview at. Tips for setting up an Excel spreadsheet was given in the previous section. Make sure that you figure out every question that you struggle with and to be ready for the similar styles of questions you will be asked in future rounds.

Good luck!