计算黑色星期五：在西方，星期五和数字13都代表着坏运气，两个不幸的个体最后结合成超级不幸的一天。所以，不管哪个月的十三日又恰逢星期五就叫“黑色星期五”-Calculation on black Friday: in the west, Friday and number 13 stands for bad luck, finally combined into two unfortunate individual super unlucky day. So, no matter which month of the 13 arrived Friday is called "black Friday"