Variation

1a) R=Resistance, S=Speed
New Resistance:
R=S3
=23
=8
So,the ratio is 8:1
b)Let R=kS^3
S=[(1+X%)^3-1]x100%=72.8%
[(1+x%)^3)-1]=0.728
(1+x%)^3=1.728
1+x%=1.2
x%=0.2
So,x=20%
2a)Let V=kr^2
300=k(2.5)^2
k=48
So, V=48r^2
b) =[(1-x%)^2-1]x100%=125%
[(1-x%)^2-1]=1.25
(1-x%)^2=0.25
1-x%=0.25開方
1-x%=0.5
100-x%=50%
x=50%

Hope can help you.
Variation is my a special skill.