7/10+5/12-1【通分】=7x6/60 +5x5/60 -1=(42+25)/60 -1=67/60 -1=1又7/60 -17/60
=7x6/60 +5x5/60 -1=(42+25)/60 -1=67/60 -1=1又7/60
7/10+5/12-1=42/60+25/60-1=67/60-1=7/60
