50×51分之1+51×52×53分之1+53×54分之1+54乘55分之1
问题描述：
50×51分之1+51×52×53分之1+53×54分之1+54乘55分之1
答
1/(50×51)+1/(51×52)+1/(53×54)+1/(54×55)
=1/50-1/51+1/51-1/52+1/53-1/54+1/54-1/55
=1/50-1/55
=(55-50)/(50×55)
=5/(50*55)
=1/550