binomial variance problem

by nerfhammer 1 min read6th Apr 201214 comments


Found in an old Kahneman & Tversky paper:

There are two programs in a high school. Boys are a majority (65%) in program A, and a minority (45%) in program B. There is an equal number of classes in each of the two programs.

You enter a class at random, and observe that 55% of the students are boys. What is your best guess -- does the class belong to program A or to program B?