How do you fix the error: fix attempt to preform arithmetic (add) on instance and number?

Hello! I've been experiencing this error with NumberValues and IntValues, I was wondering if anyone can help I guess.

local BuyAndSellAmount = script.Parent
local number = math.random(1,6)

while true do
    wait(5)
    if number == 1 then

        local numb = 1

        print("+1")
        BuyAndSellAmount = BuyAndSellAmount + numb


    elseif number == 2 then

        local numb = 0.1

        print("+0.1")
        BuyAndSellAmount = BuyAndSellAmount + numb

    elseif number == 3 then

        local numb = 2

        print("+2")
        BuyAndSellAmount = BuyAndSellAmount + numb

    elseif number == 4 then

        local numb = 1

        print("-1")
        BuyAndSellAmount = BuyAndSellAmount - numb

    elseif number == 5 then

        local numb = 0.1

        print("-0.1")
        BuyAndSellAmount = BuyAndSellAmount - numb

    elseif number == 6 then

        local numb = 2

        print("-2")
        BuyAndSellAmount = BuyAndSellAmount - numb




    end 

Also note that im currenently trying to add/subtract 2 numbers every few seconds.