Jane Street 1st round interview - any tips?

Hi,

So I have a phone interview with Jane Street sometime soon and I believe the finance interview will be highly quantitative. I am a math major as well as a finance major but haven't taken any major math classes yet; will be starting them next semester. So any tips on how I should prepare for the quant. stuff? Especially probability?

 
aachimp:
mental math is huge. even if you get all the answers right, if they feel you aren't quick enough, you're done.

I've been through quite a few interviews and I constantly get mental math questions like what's 4449, 3373 etc. Do they actually expect you to get those right or are they just looking for the process? I got the correct answer in an in person interview and I got a shocked look like I'm not suppose to actually get the number.

 
Best Response
The Tripster:
aachimp:
mental math is huge. even if you get all the answers right, if they feel you aren't quick enough, you're done.

I've been through quite a few interviews and I constantly get mental math questions like what's 4449, 3373 etc. Do they actually expect you to get those right or are they just looking for the process? I got the correct answer in an in person interview and I got a shocked look like I'm not suppose to actually get the number.

yes, you are supposed to get those right. there is no process unless it's a special case where they want you to make it easier.

for example. a^2-b^2 = (a+b)(a-b). -> 4555 = 50^2-5^2 = 2475. different example, 1218.5 = 2012 - 1.512 = 222.

if you look up the Trachtenberg speed system of mathematics and perfect it, you can really fly through huge problems like 12513*25922, etc...

There's also Vedic math techniques that work for double and triple digit multiplication.

 

i have an interview with JSC next week as well. i'm a chemistry/econ dual major and math minor. i haven't taken any intense probability, stats, and comp sci courses, however. i'm pretty much going to treat this as a practice interview for my BB rounds. i know i have little chance against the five people they want who do have all these skills.

 

Vedic math is very good. In fact when I was in high school, I came up with a method to accelerate the squaring process. i.e what is 67^2? most people would use (70-3)^2 or (60+7)^2, but you could do this too; 67 = 42, and 77 = 49, so you have 4249+60*4 = 4489. you could work the other way around only it would be minus for anything lower than 65.

 

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