# Consulting Q&A – Ask Questions on Your Career in Our Consulting Forum

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Consulting Q&A

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Tag: "case math"
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case math

## Organizing math

case math
Most recent answer on Aug 02, 2021
<p>What's the best way to keep your math organized? Draw tables? Any other tips?</p>
Hello! I wholeheartedly agree with all the great tips Erica has shared in her answers. Here are a few more I would add: 1. The specific method you use doesn't matter as long as the math is organized - so do what works ... (read entire answer)
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on Aug 02, 2021
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## Using labor productivity in calculations

case math
Most recent answer on Aug 02, 2021
<p>If labor in country 1 costs \$0.3/lb of product and in country 2 it's 8% wage rate of country 1 and 80% productivity of country 1..how do we factor in productivity to calculate the labor cost in country 2? Do you need to divide country 1's wage by 80%? If yes, why?</p>
A lower productivity increases your "effective" wages. If you want to product 1 unit of product: With 100% assumed productivity you will need X units of labor With 80% productivity you will need X/80% units of l ... (read entire answer)
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on Aug 02, 2021
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## Calculating price

case math
Most recent answer on Aug 02, 2021
<p>I'm not sure how they are calculating price here. I got the slope part, but after that? It's not a y=slope*x + b formula? Can we simplify this and just assume that since the accuracy is closer to 99%, our price should be closer to 2k, and do a proportional decrease (i.e. 2000 * 95%/99%= \$1920?) <img alt="" src="/uploads/qa/questions/11065/images/exb%202.jpeg"><img alt="" src="/uploads/qa/questions/11065/images/exb%201.jpeg"></p>
Hey there, Think about the solution like this: Each percaentage point of additional accuracy after 80% (blod test accuracy) worth \$97.5 (your slope) Our clients, test has 15 pp more than the blod test (95%-88%), ... (read entire answer)
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on Aug 02, 2021
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## Math logic

case math
Most recent answer on Jul 29, 2021
<p>Are there any useful resources to practice setting up the logic of case math problems? The word problems I've come across don't seem representative of what you get in an actual case. </p>
Hi there, I'd recommend any of the following: Casebooks (happy to provide good ones) Preplounge math drills Rocketblocks
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on Jul 29, 2021
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## Calculating edge cases

case math
Most recent answer on Jul 29, 2021
<p>If you have a table with prices increasing and adoption rates decreasing and need to find which price gives maximum profit, is it fine to calculate the profits at either ends (max price and minimum price) to say which one would yield highest profits or do you need to calculate profit at each price? Can you ask the interviewer if you can do the edge cases or if they would like you to calculate it for each? Will they tell you if it's unnecessary to calculate the profit for each price?</p>
Hey there, I will use a tactical approach. Everytime you have an exhibit with a lot of data and calculation have a look if there is a short-cut to avoid all the calculation. I will have a look at the numbers and try ... (read entire answer)
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on Jul 29, 2021
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## Fractions

case math
Most recent answer on Jul 28, 2021
<p>Math drills have exercises with adding fractions etc.,but I'm not sure I get where to use these during a case. What would be some examples of using fractions to do math easily in a case? </p>
Hi there! Adding fractions (or percentages) can come up in a variety of case types and consulting situations. An example might be a market share situation (e.g., Company A and Company B supply business customers in th ... (read entire answer)
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on Jul 28, 2021
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## Unnecessary data / columns

case math
Most recent answer on Jul 27, 2021
<p>In casebooks I sometimes see cases where there are extra columns or numbers given to deliberate confuse the candidate during calculations (you don't need to use the extra data in the equation). Does this happen even during MBB interviews? The interviewer may either verbally or via n exhibit give you extra numbers you don't need to use in your calculations?</p>
Hi there. When it comes to maths/calculation, the best way and the safest way is to organize your thinking (some may call it structure) before digging into the numbers, meaning you need to know what you're calculating a ... (read entire answer)
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on Jul 27, 2021
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## Doing calculations, in silence or speak out loud

case math
Most recent answer on Jul 26, 2021
<p>Once you communicate your approach to the interview do you need to do the calculations while saying it out loud (eg 460 times 12 equals.. XY) or can do it silently and just communicate the final result or intermediate resukts (eg revenues and costs before profit). </p>
Great question! One way to test if it should be 'out loud' or silent is, would someone following along be able to explain what I am doing? For example, 90% x \$10M is simple enough, but HOW you arrived at that 90% and \$1 ... (read entire answer)
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on Jul 26, 2021
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## Improving case flow/math

case math
Most recent answer on Jul 26, 2021
<p>Hello,</p> <p>I have a question regarding the flow while solving a case.</p> <p><br> I generally start with a good issue tree and structure that allows me to get the exhibits and math section of the case quickly. But when I get a lot of numbers I get nervous and that affects the rest of the case. I am generally good with math but I need tips to make the flow easier. I've been using mental math tools to improve my math but I would greatly appreciate any other suggestions.</p> <p>Another question is how much time should we take in math? Is it okay to do the calculations slowly or that might cause the interviewer to lose interest? Also, should I walk them through each calculation? And how open should we be to rounding numbers?</p> <p>Thanks,</p>
Hi Deniz! I think the best advice can be provided once we get to learn your specific problems. However, few points from my side in addition to the other answers that might help: Nervous: If you get nervous from ... (read entire answer)
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on Jul 26, 2021
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## Eyeballing percentage calculations

case math
Most recent answer on Jul 24, 2021
<p>Is there a way to improve eyeballing percentage calculations (eg. (5/25 = 20%) without writing down the math? Do you just memorize what % fractions constitute? (Eg 1/5 = 20%, 1/4 = 25%)</p>
I would suggest to start practicing mental math on dialy basis (many websites/apps can help), then you will come up with your own shortcuts.
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on Jul 24, 2021
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## Comparing costs across companies without doing %

case math
Most recent answer on Jul 23, 2021
<p>If Company A's total cost is 20M and company B's total cost is 16M..and cost sub-component 1 in A is 4M while, cost sub-component 1 in B is 1.6M, is it fair to compare these costs and deduce that we need to find ways to lower the 4M, WITHOUT doing a % calculation (I.e 4M/20M , 20% of total cost vs 1.6M/16M, 10% of total cost)..since the total costs are pretty close (20M vs 16M) can we skip the % calculation here? Or would interviewers expect you to do that before making such a conclusion?</p>
Hi there, Yes and no. First, General Advice: Generally, if you can eyeball something and point out that insight, do so prior to doing math! However, then suggest calculating the exact number "If that would be helpfu ... (read entire answer)
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on Jul 23, 2021
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## Cost savings with upfront costs

case math
Most recent answer on Jul 20, 2021
<p>The question asks you to calculate cost savings by switching a diesel vehicle to electric vehicle. They have given the new maintenance cost, efficiency costs and upfront/one-off costs for the electric vehicle. Can we add the upfront costs to the other 2 cost categories here? Do you ever add upfront costs to other cost categories or always treat it separately?</p>
Hi there, Am I right in thinking this is Diesel Transportation Co from the Ross casebook? :) You need to "normalize" the data. So, either upfront costs have to be turned into per unit costs, or your per unit costs n ... (read entire answer)
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on Jul 20, 2021
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## Net gains or just cost savings calculation

case math
Most recent answer on Jul 19, 2021
<p>In one case, they calculated the cost-savings from discontinuing a product (eg \$6000) and then calculated the reduction in profits (from lost sales of the discontinued product eg \$2000). Then they did Net gains = Cost savings - reduction in profit (I.e \$4000) Do we need to do this step? Typically I always see calculations with closing down a factory or any discontinuation of service on just a cost-savings basis. </p>
Hi there, This is actually a better way to do it. Even cost-cutting questions/prompts should consider net profits. Think about it logically: if you as a company cut costs and lose profits as a result, did you make a ... (read entire answer)
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on Jul 19, 2021
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## Comment on final math number for McK cases

case math
Most recent answer on Jul 17, 2021
<p>I've noticed for McK sometimes the math question isn't directly related to the goal of the client..so how could you comment on the final math answer then? For eg, if we are trying to improve quality of a restaurant service and suddenly we are calculating the additional revenue from introducing more pies on the menu..how would I comment on the additional revenue number (I could say we need to ensure the additional pies are great given our goal is better quality..but what else?) are there general levers you should always comment on when it comes to math..like how realistic this number is to achieve etc..? This seems easier to do in candidate-driven cases where there is a natural flow from one analysis to the other</p>
Hey there, Your observations are correct. In McKinsey cases, every question is almost like a mini-case in itself. To answer your question more directly, you can still create powerful implications that are relevant f ... (read entire answer)
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on Jul 17, 2021
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## Hours of operation

case math
Most recent answer on Jul 15, 2021
<p>If you have a cafe open from 7 am to 8 pm, isn't this 13 hours of operations? I would calculate it as 20 (8 pm conversion to 24h format) - 7 = 13, isn't this how you do it? I saw a prompt say it's 14 hours of operation.</p>
Hi there, Cases are not the gospel! Cases make mistakes. In fact, I see mistakes in about one our of every 2 or 3 cases. This is normal, but doesn't inherently mean the case is a bad one. 7am-8pm is indeed 13 hours
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on Jul 15, 2021
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## Calculating on an incremental basis

case math
Most recent answer on Jul 13, 2021
<p>I hear mixed opinions on this. Some say if you are calculating the change in profits (say revenues increased 20% and costs decreased 10%), it is better to calculate on an incremental basis (I.e find 20% revenues and then add 10% costs to get change in profits). But others say this might be hard to follow for a client and you may lose points for not being client friendly, so it's better to calculate old profit , then new profit and subtract the two to get the difference. That's easier to understand and follow when you communicate it. The example used here is simple but there may be calculations where there are multiple cost and revenue components that are changing. So is it better in general to avoid the incremental basis calculation (to avoid mistakes and be client friendly)</p>
Hi there, In math questions there may be multiple ways to find an answer. If you follow a formula that is correct and not significantly more complex than the one the interviewer has in mind, you should be fine. What ... (read entire answer)
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on Jul 13, 2021
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## Calculating on a per unit basis or total basis

case math
Most recent answer on Jul 12, 2021
Anonymous A asked on Jul 11, 2021
<p>If I'm given revenue and costs on a per unit basis and I start calculating profits on a total basis instead of per unit basis, would the interviewer ask me to do it on a per unit basis (if the case requires or if it's an easier approach)? Or would they just let me run with the "total" basis calculation?</p>
If I'm given revenue and costs on a per unit basis and I start calculating profits on a total basis instead of per unit basis, would the interviewer ask me to do it on a per unit basis (if the case requires or if it's a ... (read entire question)
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on Jul 12, 2021
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## Double checking math

case math
Most recent answer on Jul 09, 2021
<p>Is it ok to ask the interviewer "does that sound right" after doing your math calculations to see if you got the right numbers? Some interviewers give no verbal cues on whether you are on the right track, so can I ask this?</p>
Hi there, If you want to check if the approach is right (not only for math but in general), I would avoid to use the “Does it sound right?” statement. It will give the impression you are not confident. I would use a ... (read entire answer)
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on Jul 09, 2021
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## Percentage change

case math
Most recent answer on Jul 04, 2021
<p>Some people are great with percentages, they can just look at some number change - for eg if it changed from 550 to 900, and just say it changed by x% without putting pen to paper (especially during exhibit reading). Are there any tricks to get better at this without having to write it down and calculate the change?</p>
On this specific one, here my appraoch: Instead of trying to calculate in percentages, try to calculate in fractions, for example: percentage = (900 - 550) / 550 = 350 / 550 Then you can range the result by lookin ... (read entire answer)
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on Jul 04, 2021
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## Any good tips on how to speed up division calculations? e.g. large number divided per 365 to receive daily amount

case math Math problem
Most recent answer on Jul 02, 2021
<p>Is it accurate to use 350 instead of 365 for the numbers of days per year?</p>
Hi there, Let me help with some tricks. Let's say we have to solve 1,000,000 / 1,800. We can do the following. Cross out 0s ​10,000/18 Simplify 5,000/9 (cut in half) If rounding, get to clos ... (read entire answer)
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