2/12乘以14+2/14乘以16+2/16乘以18+2/18乘以20+1/20简便计算

说清楚步骤

2/12乘以14+2/14乘以16+2/16乘以18+2/18乘以20+1/20
=1/12-1/14+1/14-1/16+1/16-1/18+1/18-1/20 +1/20
=1/12
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