Many people do have rather poor mental math skills. You might ask yourself why mental math is important, when you can use Excel and calculators. To succeed in a management consulting interview, however, you have to know mental math. Firstly, management consulting interviews emphasize math skills, and you will get tested in detail. Secondly, in the day-to-day consulting job, good math skills are very handy. During case interviews the interviewer will often test your quantitative skills by asking questions that require some sort of calculations (e.g. during a market sizing exercise).
The top tier firms as McKinsey, Booz, Bain and BCG all require great mental math skills. This is also the case for smaller consulting boutique firms.. By doing a few minutes of practice every day, you can turn your mental math problems into a strength. Rad our tips below.
What should you prepare? The sort of math questions you might encounter are often quite simple. You have probably not used your mental math skills since high school. Sometimes a candidate is allowed to do the calculation on paper – especially if the complexity is high. You will use math skills as part of the case interview process. Say that you are answering a pricing case study. You might get a question to calculate the bottom line impact of a new price. This is a calculation that management consulting recruiters expect you to be able to solve. You need to know some quick rules for addition, subtraction, multiplication and division.
Many people will think it should be the easiest above of all calculations. But what if an interviewer asks you what 1891+1640 is, can you blurt out your answer within 3 seconds? Well, this should not be as hard as it looks if you know how to break it down and calculate them separately. Let’s break this down: 1891 needs 1200 to become 3091, so 1891+1200=3091, then you just need to plus another 440 (1200+440=1640) to get the final answer, 3091+440=3531. This process may seem long, but think about doing this out loud. As you know that the result will be 3XXX, you can firstly say 3XXX out loud. While you say it, you can finish off the rest of calculation.
Generally, the basic idea is the same with addition. Let’s try one, what is 6734-89? You could break it down like: 6734-100=6634, 6634+11=6645. Maybe you have realized what we are doing now – we are simplifying the calculation. But there are still so many ways to break one number down. The basic principles are: it’s always easy to do with hundreds and people are more familiar with addition rather than subtraction.
When it comes to multiply, many people will just surrender. It only takes a bit more time to master than addition and subtraction. Still, the basic idea is the same. What is 49*73? Notice that when we can’t find hundreds, we look for tens. Let us break it down as: 50*73=3650, 3650-73=3577. It takes more time, but still, a lot easier. When you are doing the breaking down, you will find all the calculations follow the simple rules. The only thing you need to work on is your memory. Paper is also useful as your aid.
Division takes mental math to another level. You need to find the common factor quickly when you are dividing. For example, what is 35/210? If you practice a lot, you will find the common factor is 7 right away. Then you divide both 35 and 210 by the common factor. This gives a new calculation: 5/30. Now you have 5 as the common factor, and a calculation of 1/6 shouldn’t be hard.
Set up a practice routine After you have reviewed the basics, you need to set up a practice routine so you can increase the speed of your calculations. If you have some time before the case interview, you should spend it wisely. Some ideas for practicing are:
1. During grocery shopping: Add all items in your basket before you head for the checkout counter and remember to include the decimals.
2. When travelling: A natural great way to practice currency conversion.
These examples are far from exhaustive, but the main point is that you need to build your practice into your daily routine, so it feels more natural for you to work with numbers. Hope this give you some good ideas on how to practice math.