4.7×5/2+6.3÷2/5-0.4简便计算：4.7×5/2+6.3÷2/5-0.4=4.7×5/2+6.3x5/2-0.4=5/2x(4.7+6.3)-0.4=5/2x11-0.4=55/2-2/5=275/10-4/10=271/10=27.1
