Random based upon percentage

Given a set a yet unknown values in an array/table, where each value contains a number, how would I make it so that the values with higher numbers have a larger chance of being picked?

I did this in Lua and I came up with an extremely inefficient method that didn't even work some reason:

Example:

"module.InsertTokens(5,'a')
--The function above would insert the value "a" five times into an array
module.RemoveId('a') --this is supposed to remove all values of a
print(#module.Tokens)"

2 --should be 0 --why does it return 2?? D:

function module.InsertTokens(amount, id)
    for i = 1, amount do --amount times
        print'inserting'
        module.Tokens[#module.Tokens+1]=id
    end
end

function module.RemoveId(id)
for index, v in pairs(module.Tokens) do 
    if v == id then
        print'removing' 
        table.remove(module.Tokens, index)
    end 
end
end

Is there some sort of algorithm or better logic I can use? (Also if you can, point out what I did wrong with the code above?)