一道小学分数计算题,能简算,最后得500,2100/5+2100/45+2100/117+2100/221+2100/357

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一道小学分数计算题,能简算,最后得500,2100/5+2100/45+2100/117+2100/221+2100/357一道小学分数计算题,能简算,最后得500,2100/5+2100/45+21

一道小学分数计算题,能简算,最后得500,2100/5+2100/45+2100/117+2100/221+2100/357
一道小学分数计算题,能简算,最后得500,
2100/5+2100/45+2100/117+2100/221+2100/357

一道小学分数计算题,能简算,最后得500,2100/5+2100/45+2100/117+2100/221+2100/357
原式=2100(1/5+1/45+1/117+1/221+1/357)
=2100[(1/(1×5)+1/(5×9)+1/(9×13)+1/(13×17)+1/(17×21)]
=2100×1/4(1-1/5+1/5-1/9+1/9-1/13+1/13-1/17+1/17-1/21)
=2100×1/4(1-1/21)=2100×1/4×20/21=500