练习册80) 用简便方法计算 （o.75x42.6—o.574x25+57.4)÷3

（o.75x42.6—o.574x25+57.4)÷3
=（o.75x42.6+（—57.4x0.25+57.4）)÷3
=0.75x(42.6+57.4)÷3
=0.25x100
=25