How to add a random score using math.random()?

Explained better: I am having fun with math.random() and I wanted it to forcefully add either 7, 6 or 3 points to the score variable.. Here is the script:

local Team1Score = 0
local Team2Score = 0
local conditionalvar= true

--I dont know how to do this so i just thought of the only way that might have worked..
local addon1 = Team1Score + 7
local addon2 = Team2Score + 7
local addon3 = Team1Score + 6
local addon4 = Team2Score + 6
local addon5 = Team1Score + 3
local addon6 = Team2Score + 3

-- I think it will only work in a conditional so i did this
if conditionalvar == true then
	local aryAddon = {addon1, addon2, addon3, addon4, addon5, addon6}
	randomAddon = aryAddon[math.random(1,#aryAddon)]
	return randomAddon -- now I just did this not knowing if it would work or not...
end

--now i dont know how to make it do the variable....

Sorry if it isn't explained well enough! if you have questions just comment below and ill answer.. I'm on a time crunch, but I would really like to know! Thanks for feedback!

Something like this might work out better:

local Options = {3,6,7}

local Team1Score = 0
local Team2Score = 0

local function AddToScore(Team)
	local Amount = Options[math.random(1,#Options)]
	if Team == 1 then
		Team1Score = Team1Score + Amount
	else
		Team2Score = Team2Score + Amount
	end
end

print(Team1Score)
AddToScore(1)
print(Team1Score)

Where you just have a table of outcomes, and you use math.random to choose a random outcome to add to the score.