Assign 100 percent unevenly between a variable number of items I have a variable number of web sites to which I wish to redirect traffic. I'd like to assign a bigger chance to the first one on the list than the second, and so on. For example: Site 1: 100% * * * Site 1: 60% Site 2: 40% * * * Site 1: 55% Site 2: 35% Site 3: 15% Ideally, the percentage change ratio between site 1 and site 2 should be the same as the change ratio between site 2 and site 3. Is there a formula to achieve this?

As I understand, from the comments, the goal is to fix $d$ and then require that the additive drop between sites $s_i$ and $s_{i+1}$ be $d$.

Assume $d,n$ are fixed. Then all we need to know is the amount of traffic to the first site, call it $s_1$. Then $s_i=s_1-(i-1)d$ so we compute $$100=\sum_{i=1}^n\left(s_1-(i-1)d\right)=ns_1-\frac {(n-1)(n)}2d$$

It follows that we should take $$\boxed{s_1=\frac {100}n+\frac {n-1}2d}$$

Example: $n=3,d=20$. Then $$s_1=\frac {100}3+20=53.333\dots$$ Thus in this case your numbers should be $\\{53.333,33.333,13.333\\}$. Note that the numbers you gave do not add to $100$.