So i need a chance system for a random number picker any ideas?

    local BrickEvent = game.ReplicatedStorage.Events.Gui

    BrickEvent.OnClientEvent:Connect(function(plr)
local num = math.random(1,3)
    if num == 1 then
              print("you got Critical Hit Fact")
            script.Parent.ScreenGui.Frame.HintCriticalDamage.Visible=true

     elseif num == 2 then
             print("you got Stamina Fact")
            script.Parent.ScreenGui.Frame.HintStamina.Visible=true
     elseif num == 3 then
             print("you got Jump Attack Fact")
            script.Parent.ScreenGui.Frame.HintJump.Visible=true

	            end
	wait("9")
            script.Parent.ScreenGui.Frame.HintCriticalDamage.Visible=false
            script.Parent.ScreenGui.Frame.HintStamina.Visible=false
            script.Parent.ScreenGui.Frame.HintJump.Visible=false
        end)

that's my code and almost every time i get the same one twice in a row is there any way I can add a chance system so it almost never gets the same one in a tow

you can do

local previousnum
if previousenum ~= num
	then do the code if it is diffrent
end
previousnum = num

so putting it in your script it would be

local BrickEvent = game.ReplicatedStorage.Events.Gui
local prevnum

BrickEvent.OnClientEvent:Connect(function(plr)
local num = math.random(1,3)
	if prevnum ~= num then
		if num == 1 then
			print("you got Critical Hit Fact")
	                script.Parent.ScreenGui.Frame.HintCriticalDamage.Visible=true
	        elseif num == 2 then
	        	print("you got Stamina Fact")
	                 script.Parent.ScreenGui.Frame.HintStamina.Visible=true
	        elseif num == 3 then
	        	print("you got Jump Attack Fact")
	                 script.Parent.ScreenGui.Frame.HintJump.Visible=true
	        end
		wait("9")
	        script.Parent.ScreenGui.Frame.HintCriticalDamage.Visible=false
	        script.Parent.ScreenGui.Frame.HintStamina.Visible=false
	        script.Parent.ScreenGui.Frame.HintJump.Visible=false
	        end)
		prevnum = num
	end
end

The problem lies within the nature of the math.random function. How it works is that it generates a value from x to y, with the 'seed' of the RNG (Random Number Generator) determining the outcome. Since you haven't set the seed to anything it'll spit out the same sequence every time.

To set the seed you simply use the math.randomseed function, with the only argument being the seed.

To make your script truly randomized you can just slap this line of code onto the top lines of your script, just make sure that you set the seed before you need to generate a random number.

math.randomseed(tick())

The tick function returns the timepoint at which it was called, meaning that it will be different each time it is called. Which is perfect for an RNG seed.