578-298
=578-(300-2)
=278-300+2
=278+2
=280用简便方法计算:1.3+4.25+3.7+3.751.3+4.25+3.7+3.75=(1.3+3.7)+(4.25+3.75)=5+8=13脱式计算：3.6×{2/(4/5-0.6)}