STAT 400 Spring 2011 Homework #3 (10 points) (due Friday, February 11, by 3:00 p.m.) No credit will be given without supporting work. 1. During two-and-a-half years of research, bio-psychologist Onur Güntürkün discovered that when people kiss, they turn their heads to the right roughly twice as often as to the left. (Güntürkün, O. Human behaviour: Adult persistence of head-turning asymmetry. Nature , 421, 711 , (2003).) Suppose the probability that a person would turn his/her head to the right is 2 / 3 , and the probability that a person would turn his/her head to the left is 1 / 3 . A couple is planning a kiss on Valentine’s day. Assume that their choice of which way to turn their heads is independent of each other. a) What is the probability that they would both turn their heads to the right (and kiss)? b) What is the probability that they would bump noses (i.e., choose the opposite direction to turn their heads)? Similar arguments with 3 / 4 and 1 / 4 predict phenotypic ratios of 9:3:3:1 in F 2 offspring in Mendel's dihybrid crosses. 2. From a group of 16 male and 9 female armadillos, Noah must choose two to travel on his ark. Unable to distinguish between male and female armadillos, Noah must choose at random. a)
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