Interview Questions & Reviews

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“Suppose you have two covariance matrices A and B. Is AB also a covariance matrix? Suppose that, by plain dumb luck, we also have that AB=BA. Is AB a covariance matrix under this additional…”

“10 ropes with red and blue end. red end can only connect blue end. what is the expected value of cycles?”

“class A {
    public A() {

    public void foo() {
            System.out.println("Class A");

class B extends A {
    public B(){}


“Let's say we're playing Russian roulette. The revolver has SIX barrels, THREE of which contain bullets. I give you two options:

A. Spin, shoot. Spin, shoot. Spin, shoot. (For a total of…”

“Coin Triplets Problem
Denote H for head, T for tail in a coin flip.
Flip a fair coin many times until either a pattern of HHT or HTT occurs. What's the probability that HHT occurs before HTT…”

“What is the last digit in the solution to 3^33?”

“If given X area square footage and X length of the room, what is the room's perimeter?”

“If there is an 84% chance of an event happening in an hour, what is the probability that it happens in half an hour?”

“You flip four coins. At least two are tails. What is the probability that exactly three are tails? Do this in your head, you are not allowed to write anything down for this question.”

Trader at Jane Street

Mar 6, 2012

“A has 5 fair coins and B has 4 fair coins. A wins only if he flips more heads than B does. Probability of A winning?”

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