5/9+5/12+7/12+4/9-1/5
=（5/9+4/9）+（5/12+7/12）-1/5
=1+1-1/5
=1又4/5
5/9+5/12+7/12+4/9-1/5=（5/9+4/9）+（5/12+7/12）-1/5=2-1/5=9/5
5/9十4/9十（5/12十7/12）一1/5=1又4/5
