十五分之七除以5+十五分之八x20%
=（7/15+8/15）×20%
=1×20%
=0.2
19除以五分之三除以19%
=19×5/3×100/19
=500/3
解方程
3+7%x=10
7%x=7
x=100
20%x+x=36
1.2x=36
x=30
70%x+30%x=40%
(70%+30%)x=40%
x=0.4