Update README.md

Author: dingran

README.md

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 # Quantitative interview questions and strategies
-Tips and tricks for quantitative interviews
+
+Table of content
+---
+<TBA>
+  
+# Calculus and linear algebra
+# Probability
+# Statistics
+# Programming essentials
+# Numerical methods and optimization
+# Machine learning concepts
+
+
+
+# Probability
+## Combinatorics
+- Permutation
+- Combinations
+- Inclusion-exclusion
+
+## Conditional probability
+- Bayes rule
+- Law of total probability
+ 
+## Probability Distributions
+- Expectation and variance equations
+- Discrete probability
+- Continuous probability: uniform, gaussian, poisson
+
+## Expectations, variance, and covariance
+- linearity of expectation
+- law of total expectation
+- covariance and correlation
+- independence implies zero correlation
+- hash collision probability
+
+## Universality of Uniform distribution
+- proof
+- circle problem
+
+## Order statistics
+- expectation of min and max and random variable
+
+## Graph-based solutions involving multiple random variables
+breaking stick
+meeting at the train station
+simplex
+frog jump
+
+## Approximation trick1: Central limit theorem
+- fake coin
+- monte carlo integration
+
+## Approximation trick2: Poisson paradigm
+- birthday problem, birthday triplets, near birthday problem
+- repeated draws
+
+## Poisson count/time duality
+- possion from possions
+
+## Markov chain tricks
+- various games
+- introduction of martingale