Problem Set 4 Solutions Due: Monday, February 28 at 9 PM Problem 1. Prove all of the following statements except for the two that are false; for those, provide counterexamples. Assumen 1. When proving each statement, you may assume all its predecessors (a)a =(mod n) Solution. Every number divides zero, so n (a-a), which means a a (mod n). (b)a≡b(modn) impliesa(modn)

Problem set 3 Solutions Due: Tuesday, February 22 at 9 PM Problem 1. An urn contains 75 white balls and 150 black balls. while there are at least 2 balls remaining in the urn, you repeat the following operation. You remove 2 balls elected arbitrarily and then: If at least one of the two balls is black, then you discard one black ball and put the other ball back in the urn

Problem set 2 Solutions Due: Monday, February 14 at 9 PM Problem 1. Use induction to prove that n/n for alln olution. The proof is by induction on n. Let P(n) be the proposition that the equation Base case. P(2 )is true because Inductive step. Assume P(n)is true. Then we can prove P(n +1)is also true as follows

Problem set 1 Solutions Due: Monday February 7 at 9 PM Problem 1. The connectives A(and), V(or), and =(implies)come often not only in com uter programs, but also everyday speech. But devices that compute the nand operation

1 Stencil the flea There is a small flea named Stencil. To his right, there is an endless flat plateau. One inch to his left is the Cliff of Doom, which drops to a raging sea filled with flea-eating monsters Cliff of doom

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. A couple decides to have children until they have both a boy and a girl. What is the expected number of children that they'll end up with? Assume that each child is equally likely to be a boy or a girl and genders are mutually independent Solution. There are many ways to solve

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

Problem 1. Suppose that you flip three fair mutually independent coins. Define the fol- lowing events: Let be the event that the first coin is heads. · Let be the event that the second coin is heads. · Let be the event that the third coin is heads

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