你可以发现9+99=19+89=……=49+59=108
所以原式=9+19+29+39+49+59+69+79+89+99
=108×5
=540
简便运算,越简便越好9+19+29+39+49+59+69+79+89+99
简便运算,越简便越好9+19+29+39+49+59+69+79+89+99
数学人气:704 ℃时间:2019-08-21 22:41:47
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