15-4/5÷3/2-7/15 =15-8/15-7/15 =15-（8/15+7/15）=15-1=14
3/4×14/15-3/4÷15/2 =3/4×（14/15-2/15 ）=3/4×12/15=3/5
13/15÷5/3+2/15×3/5=13/15x3/5+2/15×3/5=(13/15+2/15)×3/5=3/5
11/12×5/8÷11/12×5/8=11/12×5/8÷11/12×5/8=5/8×5/8=25/64
1又7/8-5/9-2/13÷9/26 =15/8-5/9-2/13x26/9 = 15/8-(5/9+4/9 )=7/8
5/6+2/5+8/15÷8/9 = 5/6+2/5+8/15x9/8=5/6+2/5+3/5=1又5/6
4/25÷1/99+4/25 = 4/25x99+4/25 =4/25（1+99）=16
（2/9-1/12）×（9×12）=2/9x9×12-1/12×9×12=24-9=15