How to use percentage, im kinda confused?

I made something like percentage for dropping fishes. For example, Fish 1 has 30 % to be dropped but Fish 2 has 70%. I was trying to use math.random but it didn't work. Any suggestions on how to do it( with explanation and modifying percentage). // Edit, another problem

local rod = script.Parent
local pomost = game.Workspace.PomostLvl1
local FishOdds = math.random(1,100)
local Fish1Odds = 1,30
local Fish2Odds = 31,100
db = false

pomost.Touched:Connect(function()
	rod.Activated:Connect(function()
		db = true
		if FishOdds == Fish1Odds then
			wait(1)
			print("Catched fish number 1!")
			db = false
		end
		if FishOdds == Fish2Odds then
			wait(1)
			print("Catched fish number 2!")
			db = false
		end
	end)
end)

There are a couple issues here..

• You are attempting to assign 1 variable to 2 values. You should be using a table.

• FishOdds has been defined outside of the event; therefore, shall only ever return the same thing. Define inside the Activated event to get different results every time it fires.

• You are comparing the FishOdds result incorrectly. You have used the == equivalency comparative operator when you should have used >= and <= to specify a spectrum.

• Your debounce has no condition, you are just toggling a bool which is doing nothing.

local rod = script.Parent
local pomost = workspace:WaitForChild("PomostLvl1")
local Fish1Odds = {1,30} --Use tables
local Fish2Odds = {31,100}
db = false

rod.Activated:Connect(function()
	if db then return end --Debounce condition
	db = true
	local FishOdds = math.random(1,100) --Define inside the event
	local note = " " -- <= and >= for spectrum
	if FishOdds >= Fish1Odds[1] and FishOdds <= Fish1Odds[2] then
		note = "Caught fish number 1"
	elseif FishOdds >= Fish2Odds[1] and FishOdds <= Fish2Odds[2] then
		note = "Caught fish number 2"
	end
	wait(1)
	print(note)
	db = false
end)

######Note: Not sure what you were trying to do with the Touched event..

If we wanted to calculate the probability of landing heads when flipping a coin once, we'd take the number of values that'd meet how condition (landing heads), which in this case is one, and divide it by the number of all possible outcomes, 2; so, we'd represent it as 1/2, 50%.

We want to do the same thing here, so first we'll establish the number of outcomes that'd fufill our condition. In your case, 0-30 for fish1, so 0 <= n <= 30. Next, we need to get a randomly generated number from our range, which in your case is 100, which we can do using math.random(0,100), giving us 100 possible outcomes. So, 1/30 or 30%.

if math.random(0, 100) <= 30 then
	-- spawn fish1
end

And, since Fish2's spawn rate happens to also be 70%, the probability of Fish1 NOT spawning, we can express both as

if math.random(0, 100) <= 30 then
	-- spawn fish1
else
	-- spawn fish2
end