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?
 A: There are infinite many ways. One of the ways is to use geometric sequence. For example, if $n$ denotes the number of sites then you can assign $x$ to site $n$, $2x$ to site $n-1$, $\cdots$, $2^{n-1}x$ to site 1. The sum of the percentages should be 100. Consequently, $x(1+2+\cdots + 2^{n-1})=(2^n-1)x=100$. Therefore, $x=100/(2^n-1)$. 
This is just an example. You can generate $n$ percentages randomly and assign the sorted percentages to the sites. You can use arithmetic sequence etc.
A: 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 $100$.
