Q150 我想是 B, 如錯, 請見諒!!! 2tu = 3a (a for any intergers) 2tu*3 = 3a*3 = 9a 2tu*3=(200+10t+u)*3=9a 600+30t+3u=9a (594+6)+(27t+3t)+3u=9a (594+27t)+(6+3t+3u)=9a 9(66+3t)+3(2+t+u)=9a Since the former part can be divisble by 9, so...the latter part can also be divisble by 9(without any reminders) 3(2+t+u), 3 is not divisble by 9 , so 2+t+u must be divisble by 9! -- by 会员 treewing929 (2012/2/7 21:15:30)
That 3(2+t+u) is divisible by 9 cannot guarantee that (2+t+u) can be divided by 9, but only promise (2+t+u) is divisible by 3 | 
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发表于 2012-2-8 06:22:39
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