（8/15+9/20*2/3）÷1/12
=（8/15+3/10）×12
=8/15×12+3/10×12
=6.4+3.6
=10
（0.4+2/3）/（5/6-0.75）*0.5
=16/15*0.5/（1/12）
=8/15×12
=6.4
1/4x+3/4x=1/3
x=1/3
7/16：x =7/8：32/9
7/8x=7/16×32/9
7/8x=14/9
x=16/9