69.8-(4.7+19.8)=(69.8-19.8)-4.7=50-4.7=45.34.74-8.98+15.98=4.74+(15.98-8.98)=4.74+7=11.742.5-1.98=2.5-(2-0.02)=2.5-2+0.02=0.527.2*9.9=7.2*(10-0.1)=72-0.72=71.287.2*10.1=7.2(10.0.1)=72+0.72=72.7288.8*1...72.18-（15-2.72）72.18-（15-2.72）=72.18-15+2.72=(72.18+2.72)-15=74.9-15=(75-0.1)-15=75-15-0.1=6.-0.1=59.9