Adobe acrobat form - need help!

Hi there,
 
I have just built a form in adobe acrobat 9 pro and I'm having a problem with one section and was wondering if anyone could help me or point me in the right direction?
 
Basically, in my form, there are 3 fields for beneficiary names, we'll call them "ben1" "ben2" and "ben3", with a percentage allotted field right next to them. The "X" represents the value that the user needs to input.
 
ben 1: X % percentage allotted (value can't exceed 100%)
ben 2: X % percentage allotted (value can't exceed 100%)
ben 3: X % percentage allotted (value can't exceed 100%)
 
For each beneficiary, I want there to be a restriction of 100% as the maximum value they can input. BUT, here's the issue I'm having. I want the total of all three beneficiaries to equal 100%, not more or less. For example, below, I inputted 3 figures....if all of these values are added together, the value equals more than 100%, which is wrong. Is there a way of doing this, where regardless of whether or not there is one beneficiary, two or all three, that the percentages equal 100% based on the amounts that are filled in? And, I want to make sure the values inputted aren't less than 100% either.
 
ben 1: 50 % percentage allotted (value can't exceed 100%)
ben 2: 40 % percentage allotted (value can't exceed 100%)
ben 3: 30 % percentage allotted (value can't exceed 100%)
 
My question is, what is the best way of achieving the results I would like? Is there anyone who can help me or offer me some advice, I would really appreciate it.