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1加到99的简便方法？2种解法来PK~
方法一：首尾相加乘组数：1+2+3+4......+97+98+99=（1+99）+（2+98）+......+（49+51）+50=100×49+50=4950 方法二：等差数列求和公式：99（1+99）/2=4950
常见简便计算习题精讲19/21
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