I need help understanding this part of math.random. ?

Basically I found an egg hatching tutorial and this is the chance script; Im having trouble understanding how rare each rarity actually is. Is there any way to convert these into percentages? ( without changing the code, i just want to have

--[[
	Rarities;
	1K = 25%
	500 = 13%
	300 = 6%
	100 = 3%
	1 = 1%
--]]

Not those exact percentages but something along those lines

local module = {
--Demonic
			["Common"] = {
		["Cost"] = 500,
		["Pets"] = {-- {Weight/Rarity}
			["Cat"] = {1000},
			["Dog"] = {1000},
			["Bunny"] = {300},
			["Bear"] = {300},
			["Rare Pet"] = {100},
			["Unobtainable Pet"] = {1},
	
		},
			}
			}
		

return module
--[[
	Rarities;
	1K = Common
	500 = Uncommon
	300 = Uncommon
	100 = Rare
	1 = Extreme
--]]

and here is where the math.random is:

local function ChoosePet()
	local Chance = math.random(1,TotalWeight)
	local Counter = 0
	for i,v in pairs(Pets) do
		Counter = Counter+v[1]
		if Chance <= Counter then
			return i
		end
	end
end

here is the full script in case you need it;

local ProximityPromptService = game:GetService("ProximityPromptService")
local RS = game:GetService("ReplicatedStorage")
local Eggs = require(RS:WaitForChild("Eggs"))
local Data = Eggs[script.Name]
local Cost = Data["Cost"]
local Pets = Data["Pets"]


local Buy = game.Workspace.Eggs.Common
local Cost1 = Buy:WaitForChild("Cost")
local CD = Buy.Buy:WaitForChild("ProximityPrompt")
local CostGUI = Cost1:WaitForChild("Am")
local CostText = CostGUI:WaitForChild("TextLabel")

CostText.Text = Cost.." Coins"

local TotalWeight = 0
for i,v in pairs(Pets) do
	TotalWeight = TotalWeight + v[1]
end

local function ChoosePet()
	local Chance = math.random(1,TotalWeight)
	local Counter = 0
	for i,v in pairs(Pets) do
		Counter = Counter+v[1]
		if Chance <= Counter then
			return i
		end
	end
end

CD.Triggered:Connect(function(Player)
	local Stats = Player:WaitForChild("leaderstats")
	local Coins = Stats:WaitForChild("Coins")
	local open = Player:WaitForChild('OpenValue')
	local got = Player:WaitForChild('GotPet')
	if Coins.Value >= Cost then
		Coins.Value = Coins.Value - Cost
	open.Value = 'Open'
	got.Value = ChoosePet()
	local findpet = Player:WaitForChild('Pets')
	local sqq = findpet:FindFirstChild(got.Value)
     sqq.Value = 'owned'
		wait(5)
	open.Value = 'Close'
	got.Value = ''
	end
end)