CMPSCI 240: Reasoning About Uncertainty

David Mix Barrington

Fall, 2009

Questions and Answers on Homework Assignment #1

HW#1 is due on paper in class, Monday 21 September 2009

Question text is in black, my answers in blue.

• Question 1.1, posted 20 September: Part (a) of Problem 6.2.3 looks too easy to me. There isn't any way to have a "111" in a string of length 0, 1, or 2, so are all those answers "zero"?

  Yes, exactly. Part (a) is easier, and in parts (b), (c), and (d) you have to think. Of course you can find the answer for lengths 4, 5, and 6 by listing all the sequences and counting how many have "111" in them, but that method wouldn't scale well to larger lengths. The method outlined in the hints does scale to larger lengths -- use it, and if you like use the direct counting to check your answer.

Last modified 20 September 2009