Hey,
On the preplounge math tools -some multiplications are between 20 and 99.
EG 24 x 45 / 63 x 18 / 91 x 22
How do you do these in your head fast?
cheers!
Get Active in Our Amazing Community of Over 451,000 Peers!
Schedule mock interviews on the Meeting Board, join the latest community discussions in our Consulting Q&A and find like-minded Case Partners to connect and practice with!
Question merged
This question is read-only because it has been merged with Tips to do big multiplications in my mind.
This question is read-only because it has been merged with Tips to do big multiplications in my mind.
Times Tables 20-99
Overview of answers
Upvotes
Best answer
Hi Anonymous,
my advice here: do NOT do such calculations in your head during an interview! You will not get ANY bonus points for this! The only two things that count are
(1) You are consistently correct in your math
(2) You can be easily followed
For this, do WRITTEN calculations. When properly done, it barely takes more time. But it is a much clearer way of communicating - and this is what is much much more important than speed! Doing math in your head is absolutely not client friendly: the interviewer will assume that this is how you will also act with clients. If the client can not follow you (because you are doing math in your head and are not being explicit with it, it is your fault!
That being said - it is certainly not harmful to practice such multiplications tables. But in the interview, please do the math properly in WRITTEN form!
Cheer, Sidi
Upvotes
How I would do the examples you provided:
24*45 = 10*45*2 + 4*45 = 900+180=1080
63*18 = 63*20-(63*2)=1260-126=1,134
91*22=90*22 +1*22 =90*20+90*2 +22 = 1800+180+22=2,002
In general, I try break up numbers into smaller segments that are easier to manage. It also depends if it's easier to subtract (as I did in the second example above) or just add up the various segments (as I did in example 1).
In general, just a lot of practice with this will get you a lot better and enable you to solve questions like this in your head in a short amount of time - but I would still write it out in an interview to be 100% sure!
Upvotes
Hi,
I use the following method and recommend it to all of my students:
https://www.youtube.com/watch?v=6ndkkPZYJHo
You can learn to do it on paper fast in 1-2 hours, and it will take couple of days to train doing it mentally.
Other useful tools:
1) Learn how to work with zeros. Best way - always use 10^power instead of zeros
Example:
300x9000 = 3*10ˆ2 x 9*10ˆ3=3x9*10ˆ(2+3)=27*10ˆ5
Handwritten it looks not that complicated. If you get used to writing all the numbers that way, you will never loose zeros and all multiplications/divisions will be replaced with + or -.
2) Learn the division table up to 1/11 (i.e. 5/6 = 83.3%). It will help you calculate any percentage problems
Best
(edited)
Upvotes
Hi Anonym,
you may have a look at this video:
https://www.youtube.com/watch?v=6ndkkPZYJHo
best regards
Upvotes
Related Cases
Expert case by Francesco
Our client is SmartBridge, a nonprofit educational institution offering face-to-face tutoring services. The client operates in the US.The mission of SmartBridge is to help as many students as possible to complete studies and prevent that they drop from the school system, in particular in disadv
...
Our client is SmartBridge, a nonprofit educational institution offering face-to-face tutoring services. The client operates in the US.The mission of SmartBridge is to help as many stude
...
(Open whole case)
31.6k
Times solved
Advanced
Difficulty
Expert case by Francesco
Style:
Our client is a BlissOttica, an Eyewear Manufacturer that is looking to reach a 10% increase in profits. How would you help our client?
Our client is a BlissOttica, an Eyewear Manufacturer that is looking to reach a 10% increase in profits. How would you help our client?
(Open whole case)
13.6k
Times solved
Intermediate
Difficulty