By Wei Yiyang Philip In the lobby of the Tower of the Juche Idea in Pyongyang, tourist Emily Liu buys a ticket to go to top of the 150-meter-high structure. It costs 300 North Korea won, however, since foreign tourists are not allowed to use North Korean currency, she pays the equivalent official value of 20 Chinese yuan. But Emily’s 20 yuan is actually worth far more than 300 won. Compared with the official rate of 15 won to one Chinese yuan set by the North Korean government, the value of yuan on the North Korean black market averages at around 1,250 won to 1,350 won, That means her 20 yuan is at...