5.78+3.4-3.78=2+3.78+3.4-3.78=0+2+3.4=5.4
简便计算5.78+3.4-3.78=5.78-3.78+3.4=2+3.4=5.4
原式=5.78-3.78+3.4 =2+3.4 =5.4
5.78+3.4-3.78=5.78-3.78+3.4=2+3.4=5.4