(20-8×25%)÷0.04
=(20-2)÷0.04
=18÷0.04
=450
0.23×二又二分之一+0.77÷40%
=0.23x2.5+0.77x2.5
=(0.23+0.77)x2.5
=1x2.5
=2.5
十九分之五×37-十九分之五÷三十七分之一
=5/19x37-5/19x37
=0