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Unformatted text preview: University of Illinois Spring 2010 ECE 313: Problem Set 1: Solutions Sets, Events, Axioms of Probability and Their Consequences 1. [Subsets of a finite set] (a) The subsets of Ω = { ω 1 ,ω 2 ,ω 3 ,ω 4 } are Subsets of size 0: ∅ Subsets of size 1: { ω 1 } , { ω 2 } , { ω 3 } , { ω 4 } Subsets of size 2: { ω 1 ,ω 2 } , { ω 1 ,ω 3 } , { ω 1 ,ω 4 } , { ω 2 ,ω 3 } , { ω 2 ,ω 4 } , { ω 3 ,ω 4 } Subsets of size 3: { ω 1 ,ω 2 ,ω 3 } , { ω 1 ,ω 2 ,ω 4 } , { ω 1 ,ω 3 ,ω 4 } , { ω 2 ,ω 3 ,ω 4 } Subsets of size 4: { ω 1 ,ω 2 ,ω 3 ,ω 4 } = Ω There are 16 = 2 4 subsets of the set Ω of 4 elements. 15 = 2 4 1 of them are nonempty subsets. (b) OK, OK, geez, some people are never satisfied ... (c) By checking our answers in parts (a) and (b), we see that there is: 1 subset of size 0 and 1 subset of size 4 0 = 4, 4 subsets of size 1 and 4 subsets of size 4 1 = 3, and lastly 6 subsets of size 2 with 4 2 = 2. For general n , whenever we choose a subset of size k , there is a unique subset of size n k that is left out. That is, for every subset of size k , there is exactly one corresponding, complementary subset of size n k , so the total number of subsets of size k is the same as the total number of subsets of size n k . (d) i. The vector { 1 , 1 ,..., 1 } corresponds to Ω. The vector { , ,..., } corresponds to ∅ . The nbit vector with each bit flipped with respect to A corresponds to A c ....
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This note was uploaded on 04/20/2010 for the course ECE ECE 313 taught by Professor S during the Spring '10 term at University of Illinois at Urbana–Champaign.
 Spring '10
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