①1/4:x=1/8:1/10
1/8x=1/4×1/10
x=1/40÷1/8
x=1/5
②5/x=30:3
30x=5×3
x=15÷30
x=1/2
③3/4:1/8=x:2
1/8x=3/4×2
x=3/2÷1/8
x=12
④6.5:x=3.25:4
3.25x=6.5×4
x=26÷3.25
x=8
⑤1.5:3/4=0.36:x
1.5x=3/4×0.36
x=0.27÷1.5
x=0.18