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#2
08 ¾ÄÉÀÒ¤Á 2014, 22:00
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¾Í¹Ñ¡àÃÕ¹àÅ×Í¡¨¹¤Ãº·Ø¡¤¹ µÑÇàÅ¢µÑé§áµè $1-30$ ¨Ð¶Ù¡àÅ×Í¡ËÁ´
ÁÕ¼ÅÃÇÁà»ç¹ $1+2+3+...+29+30 = \frac{30*31}{2} = 465$ ·Ø¡¤ÃÑ駷ÕèàÅ×Í¡¨Ðµéͧ $-1$ ´éÇ áÅÐÁÕ¡ÒÃàÅ×Í¡ $29$ ¤ÃÑé§ ¨Ö§µéͧźÍÍ¡´éÇ $29$ àÅ¢µÑÇÊØ´·éÒº¹¡Ãдҹ ¤×Í $465-29 = 436$ 
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