## HCOL 196, January 21, 2011

I assigned a problem set, due next Wednesday. The first part (Fermi problems) is to be done in your group, one paper from each group. The second is to be done individually, so I will get eleven sets of coin tosses, some fake and some real.

We had a little quiz and discussed the results. Some of the questions were designed (with varying success) to illustrate that the way identical questions are phrased (gain, loss; saving lives, losing lives; etc.) can change the results. Some were on basic probability ideas. We will discuss the one remaining question on Monday, so be sure to bring your paper with you.

The blackboard had two pictures. One showed why it is less likely that the young bank teller would also be “socially concerned” in the ways the question asked.

The other showed why in the taxicab problem, the probability that the witness correctly identified the cab as blue is around 41%. Some guessed in the 12-20% range, others in the 70-80% range, but no one got close to the correct answer. The tree diagram I drew will be one of our useful tools in this course.

I notice in this chart that I incorrectly put an “X” (meaning “ignore”) next to the third branch of the tree, which represents “Says blue, correct”. It should have been on the last branch (“Says green, mistake”).

See you Monday