The Math They Don't Teach at Wharton

Mental math on Wall Street – what does that actually look like in this day and age, and why should aspiring professionals spend their precious time on it?

Interviewing for finance is tough - all smart candidates, all took modeling courses, all did mock interviews and are ready for "Tell me about yourself", "Why do you want to work in [insert group name]", and they all look the part – although at least one will now show up in sneakers, prompting an eye roll from the few of us with gray hairs. Often, the decision comes down to an intangible like "Who seemed most excited about doing a great job here?" or "Who seemed to have the best communication skills?", but also "Who seemed the smartest?"

I can't tell you what other firms ask, but we always include quantitative discussion in our process – my go-to exercise is to let them pick a recent deal from their deal sheet, they go through the deal metrics, and I'll ask a softball, like "Was that a good deal for the buyer?", "Was that a good deal for the lender?", something like that. They usually answer yes, but then we twist it – "What if the price was $140mm, not $120mm – would it still have been a good deal? Walk me through it?" Some candidates can do this very naturally – and these are usually the ones who end up at the top of the list; most others kind of muddle through and eventually get to a passable answer. An embarrassing number just can't do it, even after we simplify the numbers or even the problem setup several times.

So what answer are you looking for in that example?

Well, we don't know the rest of the numbers, but let's say the candidate had said that post-synergies EBITDA was $9.0mm - a good answer might be to explain that at $120mm, the acquisition is priced at 13.3x, which is accretive to the acquirer's valuation at 15x, but at $140, pricing would be dilutive at 15.5x. 120 divided by 9 and 140 divided by 9 should be pretty easy mental calculations.

We'll get to FiveMinuteFox in a minute, but after interviews – once you're "in" and you get hired – does mental math still matter after that?

Yes! It definitely matters – the example I gave you for the interview question is exactly how we discuss deals every week in our IC screening meeting – "They countered our $120 bid at $140, how should we respond?" None of us are running back to our computers to look at spreadsheets. And frankly when we debrief at the end of interview day, every senior person around the conference table can process these numerical questions that we posed to the candidates. Especially when you get more senior, where business actually takes place is in the real world – work lunches, conferences, the golf course. As more of your workload shifts to new business origination, you increasingly rely on your internal ability to process the deal numbers – it has to become second nature.

So you're saying that you and all senior professionals in your group have this ability – if everyone gets there eventually, then why spend time training this with an app?

Actually I think you've misunderstood! Everyone does not get there eventually. The promotion process is a funnel – only the best people advance at each stage. And by the way, this is just one skill you need – to get to a senior level, you have to have great quantitative ability, but you also need to have great communication and negotiation skills, be a great team player, hard worker – you can fill in the rest of that list. But this is not a skill that is actively developed anywhere that I'm aware of and you don't get a lot of reps sitting at your computer. Over the years, many younger professionals have asked me how they can get better at this and I have unfortunately never known of a good resource to recommend. That's why I created FiveMinuteFox.

OK, FiveMinuteFox – what is it and why are you, a middle-aged MD, creating an app in the first place?

FiveMinuteFox is a mobile app, available for iPhone and Android, that progressively develops the mental math skill that I've been talking about. It's simple – you just click start and each day automatically starts with basic warm-up problems, and then advances through the various levels based on how you're doing over the day. The first 22 levels include techniques for multiplication, division, addition, subtraction – the skills complement each other, so after a few weeks, users may feel like everything is suddenly coming together all at once – an amazing feeling.

Levels 23–30 are the Premium levels and include questions in business, corporate finance, real estate, and fixed income contexts. Each question includes explanations of both the math setup and the underlying concepts. It's an excellent review for interview week – a few lightning rounds a day could be a great last minute confidence booster.

This trainer alternates between helping you memorize "low hanging fruit" content, like the multiplication table up to 20×20 and common fractions up to denominator of 18, and actual calculation and estimation practice. This limited memorization unlocks calculation efficiency, and the alternating format breaks up the intensity and gives each session more runway.

Why did I create this? Writers have a saying that everyone has at least one story in them. Last summer I injured my knee and needed something to replace my early morning gym routine. I've always loved computer science and immediately thought of this. This math resource is my "one story".

So this app is for junior professionals in the finance industry?

Yes, definitely for them, but also for VP-level and even senior professionals. After a few weeks of practice, I was surprised by how much smarter and better at my job even I feel.

It's built for finance, but anyone who works with numbers could benefit.

You said when we spoke earlier that this was "the math Wharton doesn't teach you" – is that true?

Actually I have no idea. I hope so! I did graduate from Wharton over two decades ago, and they didn't teach this back then. I entered the investment world feeling extremely prepared. I remember my coursework included four different classes that were oriented around valuing options. It seemed like overkill at the time, but most executive decisions are essentially an options evaluation of some kind. The option framework became second nature at Wharton and I credit much of my success to that training. But don't sleep on mental math!

For readers who want to try FiveMinuteFox, how should they start?

They can search for FiveMinuteFox at the App Store or Google Play store, or use links at FiveMinuteFox.com.

The app is ad-free and the free version includes levels 1–22. The Premium version includes the specialty levels 23–30 as well as full access to practice mode to focus on individual levels. All Premium subscriptions include a free 1-month trial. Good luck with your careers and I hope you enjoy using the app!

Note: As of February 2026, U.S. pricing for Premium is $4.99/month or $29.99/year.