Maybe something like this?
1. Make a variable like "TotalObjects".
2. Run a loop that makes TotalObjects increment by 1 for each existing object.
3. Run another loop for every object, with another variable like "TemporaryTotalObjects" that is initially equal to TotalObjects.
4. In this second loop, if TemporaryTotalObjects is more than 30% of TotalObjects, assign it to the value you want 70% of your objects to have. If TemporaryTotalObjects is less than or equal to 30%, give them the other variable.
5. Decrement TemporaryTotalObjects each time the loop runs.
So, for example, if you have ten objects:
TotalObjects = 10
TemporaryTotalObjects = 10 for Object #1, so its variable is 1.
TemporaryTotalObjects = 9 for Object #2, so its variable is 1.
TemporaryTotalObjects = 8 for Object #3, so its variable is 1.
TemporaryTotalObjects = 7 for Object #4, so its variable is 1.
TemporaryTotalObjects = 6 for Object #5, so its variable is 1.
TemporaryTotalObjects = 5 for Object #6, so its variable is 1.
TemporaryTotalObjects = 4 for Object #7, so its variable is 1.
TemporaryTotalObjects = 3 for Object #8. TemporaryTotalObjects is now less than or equal to 30% of TotalObjects, so Object #8, #9, and #10 get 2 as their variable.
I hope that makes sense. That's just off the top of my head.