Choosing Rarity:An Exercise in Stopping Times

摘要

Let's play a computer game. You will see on your computer screen thirteen envelopesin one of two colors: red or blue. The envelopes will appear one by one in randomorder. Each envelope will be visible for 10 seconds and then will disappear forever.You know that there will be five envelopes of one color and eight of the other, andeach of the five envelopes contains