应该是51又1/4吧
41又1/3x3/4+51又1/4x4/5+61又1/5x5/6
=（40+4/3）x3/4+（50+5/4）x4/5+（60+6/5）x5/6
=40x3/4+4/3x3/4+50x4/5+5/4x4/5+60x5/6+6/5x5/6
=30+1+40+1+50+1
=123
如果是51又3/4的话
41又1/3x3/4+51又3/4x4/5+61又1/5x5/6
=（40+4/3）x3/4+（50+7/4）x4/5+（60+6/5）x5/6
=40x3/4+4/3x3/4+50x4/5+7/4x4/5+60x5/6+6/5x5/6
=30+1+40+7/5+50+1
=122+7/5
=123又2/5