52.47-10.38-6.74=52.47-（10.37+0.01）-6.74=52.47-10.37-0.01-6.74=42.1-（6.74+0.01）=42.1-6.75=42.1-（7-0.25）=42.1-7+0.25=35.1+0.25=35.35
把它们变成整数再算减法得数后两位加小数点
