六年级简算
2/11×13+2/13×15+2/15×17+2/17×19+1/19
参考答案:原式=2*1/2*(1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19)+1/19
=(1/11-1/19)+1/19
=1/11
2/11×13+2/13×15+2/15×17+2/17×19+1/19
参考答案:原式=2*1/2*(1/11-1/13+1/13-1/15+1/15-1/17+1/17-1/19)+1/19
=(1/11-1/19)+1/19
=1/11