16.7*2.1-10.8=16.7*（2+0.1）-10.8=16.7*2+16.7*0.1-10.8=33.4+1.67-10.8=24.27
16.7*2.1-10.8=16.7*2+16.7*0.1-10.8=33.4+1.67-10.8=35.07-10.8=24.27
