selection based on percentage weighting

Question

I have a set of values, and an associated percentage for each:

a: 70% chance
b: 20% chance
c: 10% chance

I want to select a value (a, b, c) based

Answer 1

1. Let T = the sum of all item weights
2. Let R = a random number between 0 and T
3. Iterate the item list subtracting each item weight from R and return the item that causes the result to become <= 0.