Hi Jason,

The UT method can be used only for a 2 digit multiplier. The practice questions 13 to 18 will be updated in the next edition.

In the Vitruvian Method you would first do 667 x 386 and then 671 x 386. You should then combine the results together.

Let me know if this clarifies.

Hi Stephen,

Where you draw the line will depend on the number of digits in the flag. If the flag has one digit, then you will draw the decimal line after one digit from the right.

In your example 1 is the pole and 3 is the flag. The flag is a one digit number which is 3. So you will draw the line between 2 and 4 in 64924 (i.e 6492|4).

If you divide 64924 by 224 then where you draw the line will depend on how you create the flag and the pole.

If in 224 you make 22 the pole and 4 the flag, then you will draw the line between 2 and 4 in 64924 (i.e 6492|4) because the flag 4 is only one digit.

If in 224 you make 2 the pole and 24 the flag, then you will draw the line between 9 and 2 in 64924 (i.e 649|24) because the flag 24 is two digits.

Hope this clarifies.

Hi Akiva,

The denominator in your code does not include cases where the DS method correctly predicts a calculation as incorrect.

I have updated your code to reflect this and you can find the notebook here: https://github.com/abhivr/public_repo/blob/main/Digit_Sum_Checker.ipynb

When I wrote the book & created the course, I estimated the accuracy of the DS method using simple probability.

The digit sum can only be a number between 1 to 9. So there are 9 possible values.

8 of these 9 possible DS values will help you catch an error in the calculation without an issue.

One out of these 9 possible values is the DS of the correct answer but it can also be the DS of the incorrect answer.

So there are actually a total of 10 possible values for the Digit sum (9 Correct DS + 1 Incorrect DS) with one number repeating in Correct DS and Incorrect DS.

So 9 / 10 (90%) the DS method correctly predicts the calculation as incorrect & correct. But 1/10 times the DS method predicts the calculation is correct when it is actually incorrect.

Hope this clarifies.

Here are the steps:

We are trying to multiply

= 67 x 8.

We break down 67 into (70 – 3). So we get:

= (70 – 3) x 8

Multiplying the individual numbers we have.

= 560 – 24

LR Subtraction without Round Up. 

Here we subtract left to right.

560 – 24 = _ _ _

First number is 5 so it becomes the first digit of the answer.

560 – 24 = 5 _ _

Second digits is 6 – 2 = 4 it becomes the second digit of the answer.

560 – 24 = 5 4 _

We cannot subtract 0 – 4 so we must borrow 1 from the existing answer 54 so it becomes 53.

560 – 24 = 53 _

Now we subtract 10 – 4 to get 6 which is the last digit of the answer.

560 – 24 = 536.

Alternative LR Subtraction with Round Up. 

If you want to do the LR Subtraction with round up, then here are the steps. To recap we are trying to subtract

560 – 24 = _ _ _

We can round up 24 to 30 so the equation becomes:

560 – (30 – 6) = _ _ _

530 – 30 + 6 = _ _ _

We subtract 560 – 30 to get 530

560 – 30 = 530.

We add the amount we rounded up which is 6 to get 536.

530 + 6 = 536.

536 is the final answer for 67 x 8.

Hope this clarifies.

You must alternate between odd and even.

For example let’s take

9876.1234

Odd is marked as O.

Even is marked as E.

9 8 7 6 . 1 2 3 4

E O E O . E O E O

You start alternating from the left of the decimal place which is odd.

Hope this clarifies

Hi C,

I prepared for case study interviews myself. Originally I was trying to get into Management Consulting (McKinsey, Bain), then somehow I got into analytics which also required the use of case studies.

I would suggest you post this question in Management Consulting Facebook groups. You will surely find someone there.