51又1\4×4\5+61又11\5×5\6+71又1\6×6\7
=(50+5/4)*4/5+(60+6/5)*5/6+(70+7/6)*6/7
=50*4/5+5/4*4/5+60*5/6+6/5*5/6+70*6/7+7/6*6/7
=40+50+60+1*3
=153