Math Quiz — NYT Learning Network

Through Math for America, I am part of an ongoing collaboration with the New York Times Learning Network. My latest contribution, a Test Yourself quiz-question, can be found here

Test Yourself Math — April 22, 2013

This question is about the online currency Bitcoin.  The value of a Bitcoin recently dropped nearly $160 from a record high of around $266.  Approximately how much total value did all the Bitcoins in circulation lose?