①[7/15]+[3/5]-[3/10]
=[14/30]+
18
30−
9
30
=[23/30]
②[8/25]+[2/5]-[13/50]
=[16/50]+
20
50−
13
50
=[23/50]
③[5/12]+[3/7]-[5/12]
=[5/12]-[5/12]+[3/7]
=[3/7]
④[11/15]+[2/7]+[4/15]
=（[11/15]+[4/15]）+[2/7]
=1[2/7]
①[7/15]+[3/5]-[3/10]
=[14/30]+
18
30−
9
30
=[23/30]
②[8/25]+[2/5]-[13/50]
=[16/50]+
20
50−
13
50
=[23/50]
③[5/12]+[3/7]-[5/12]
=[5/12]-[5/12]+[3/7]
=[3/7]
④[11/15]+[2/7]+[4/15]
=（[11/15]+[4/15]）+[2/7]
=1[2/7]