数学题之53

用递等式计算。
1. 15/4*12/5-12/5/120%

=9-2
=7

2. 100.1-（2.625+0.425）*30

=100.1-3.05*30
=100.1-91.5
=8.6

3. 99/{23/4-（9/5+21/5*2/7）}
=99/[23/4-3]
=99/11/4]
=36

4. （1/4+3/8）/（1-3/10）

=5/8/(7/10)
=25/28