A friend I met in China a few weeks ago is traveling in Vietnam for the next month. He texted us to say the dong is 21,000 to $1 which is mind blowing. But it immediately made me think of a great way to talk exchange rates with my students such as in the graph above. It also brings up the talk of inflation and planned economies. If you care, here is an Economist article on the topic and here is a currency converter. Dave paid $4 for some Cokes and ended up forking out 85,000 dong!