1 Conditional Expectation and Total Expectation There are conditional expectations, just as there are conditional probabilities. If R is a random variable and e is an event, then the conditional expectation Ex(r e)is defined

Problem 1. The following two parts are not related. Try them, to make sure you un- derstand the jargon of random variables distributions, probability density functions, etc. Ask your TA if you don't understand/remember what some phrase means. (a)Suppose X1, X2, and X3 are three mutually independent random variables, each having the uniform distribution

The Law of Total Probability is handy tool for breaking down the computation of a prob- ability into distinct cases. More precisely, suppose we are interested in the probability of an event E: Pr(). Suppose also that the random experiment can evolve in two different ways; that is, two different cases X and X are possible. Suppose also that it is easy to find the probability of each

Problem 1. Find closed-form generating functions for the following sequences. Do not concern yourself with issues of convergence

Notes for Recitation 15 Problem 1. Learning to count takes practice! (a)In how many different ways can Blockbuster arrange 64 copies of 13 conversations about one thing, 96 copies of L'Auberge Espagnole and 1 copy of Matrix Revolutions on a shelf? What if they are to be arranged in 5 shelves?

Guessing a particular solution. Recall that a general linear recurrence has the form: f(n)=a1f(n-1)+a2f(n-2)+…+aaf(n-d)+g(n) As explained in lecture, one step in solving this recurrence is finding a particular solu- tion; i.e., a function f(n)that satisfies the recurrence, but may not be consistent with the boundary conditions. Here's a recipe to help you guess a particular solution:

1 Sums and approximations Problem 1. Evaluate the following sums Solution. The formula for the sum of an infinite geometric series with ratio 1 /2

1 RSA In 1977, Ronald Rivest, Adi Shamir, and Leonard Adleman proposed a highly secure cryp- tosystem(called RSa)based on number theory. Despite decades of attack, no significant weakness has been found (Well, none that you and me would know.)Moreover, RSA has a major advantage over traditional codes: the sender and receiver of an encrypted

1 The pulverizer We saw in lecture that the greatest common divisor(GCD)of two numbers can be written as a linear combination of them. That is, no matter which pair of integers a and b we are given, there is always a pair of integer coefficients s and t such that

Random variable Weve used probablity to model a variety of experiments, games, and tests. Through out, we have tried to compute probabilities of events. We asked for example, what is the probability of the event that you win the Monty Hall game? What is the probability of the event that it rains