The number is 78. || 150802 极限挑战第八集 || Go Fighting Ep. 8
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Lay was told to pick a number, he picked the number 78. There were numbered flags on the island, Show Luo, Sun Honglei, and Wang Xun were supposed to guess which number Lay had picked. Lay couldn't tell them directly, so obviously the second best thing is obviously to sing peking opera. The rest is self-explanatory, I hope.