2又2分之1+4又5分之1-1又10分之3+15分之2
=5/2+21/5-13/10+2/15
=75/30+126/30-39/30+4/40
=166/30
=83/15=5又8/15
5又20分之9-【1又10分之7+4分之1 】+3分之2
=129/20-(17/10+1/4)+2/3
=129/20-(34/20+5/20)+2/3
=129/20-39/20+2/3
=9/2+2/3
=27/6+4/6
=31/6=5又1/6