Errata: Known Errors in "Heard on The Street" |

- Posted August 8, 2018: The answer to Question 1.57 (choose p to maximize my payoff given that my opponent will
choose p'(p)) is not correct. The first nine lines are correct, down to Equation D.14. After
that the answer is simply incorrect and should be ignored.
In fact, my opponent looks at my payoff -20pp'+9p+9p'-4 and sees that it may be written as p'(9-20p)+9p-4. For fixed p, my opponent sees a linear function b.p'+a, where the coefficient is b=(9-20p) and the intercept is a=9p-4.

If b>0, my opponent wants to minimize b.p'+a and chooses the lowest possible p' value (p'=0). In this case, the payoff is a=9p-4. Note, however, that b>0 implies 9-20p>0 implies p<9/20. So, the payoff is a=9p-4<81/20-4=$1/20 (So, I get a payoff strictly less than $1/20).

If b<0, my opponent wants to minimize b.p'+a and chooses the highest possible p' value (p'=1). In this case, the payoff is 5-11p. Note, however, that b<0 implies 9-20p<0 implies p>9/20. So, the payoff is 5-11p<5-99/20=$1/20 (So, I get a payoff strictly less than $1/20).

If, however, b=0 (i.e., p=9/20), then my payoff is 9p-4=$1/20 for every p' value, which is superior to all of the above. So, I want to choose p=9/20.

- "Descartes' Rule of Signs" is spelled incorrectly as "Descarte's Rule of Signs" in three places (pp. 128, 130, 302).
- There is a typo on page 229. The equation on the last line should read "E(Nt) = pt · 1 + (1 − pt) · [1+E(Nt)]." The answer is otherwise correct.

- None yet.

- Posted October 7, 2015. Middle of page 97 "k=2,...n" should be "k=1,...,n". Page 98, "tirangle" should be "triangle."
- Posted October 16, 2015. Question 1.69 on p22. An "even number of heads" is what the interviewer wrote, but that is ambiguous (it is not about odd versus even). What he meant was "the same number of heads"
- Posted December 4, 2016. Answer 4.1 p199. First two equations should use x instead of v.
- Posted December 4, 2016. Last line p.226 "to rare" should be "too rare"
- Posted December 4, 2016. p.255 Peijnenburg and Atkinson 2013 is accidentally indented in the references. It is there but easy to miss.
- Posted April 6, 2016. p.20 Q1.59 "three men and one women" should be "three men and one woman"

- Posted January 23, 2015. In the third solution to the 90-coin problem (Q1.18 of the 15th edition, but appearing in earlier editions also), I mistakenly overlooked a case. In the case where A and B do not balance, and I swap the {27}s, it is possible that the scales tilt the opposite way. In this case, {27}B contains the coin known to be heavy or known to be light. Similarly if you go to the next step and swap {9}s.

- Posted July 24, 2012: Answer 1.6 on page 59 should say 15 plusminus 10 = 5, or 25. These correspond to S=10, or S=50. The case S=10 has a physical interpretation where the 5x10 box touches the circle on the other side of the square, but that is not consistent with the picture.

- Posted Sept 3, 2009: Question 1.16 about the ants is mis-stated. In the original question the ants can only walk parallel to the edge of the ruler. As such, they can only ever meet head on. With this amendment, the given answer is correct. Thank you to Craig Smith for finding this.
- Posted May 20, 2010: Answer 4.5 on page 191 says that 8/3 is the same as 2 1/3. Obviously 8/3 = 2 2/3.
- Posted November 24, 2010: Question 4.10 on page 37 is not worded quite clearly enough. There are multiple interpretations. My interpretation is that the game could be played repeatedly where the guest reveals a door to be empty.

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