1. 口算

2.1+0.2=       0.3+0.7=        3.6+1.6=          7.5-0.5=

2.13-0.02=     3.51+0.2=       102.03+5.3=       1.12-1.02=

4.5-0.01=      3.7-0.9=          0.9-0.32=         1.38-0.28=