How to convert string to operator?

I'm trying to make a math equation generator. There will be 2 numbers and one operator(+, -, /, *). I know how to randomly generator the 2 numbers, but I do not know how to randomly pick the operator. Here is my code for randomly picking an operator.

local operators = {'*', '/', '+', '/'}
local operator = nil

local function RandomOp ()
	local operator = operators[math.random(#operators)]
end

The problem I have is that the operator is returned as a string. I want to store the answer of the equation as a value, but obviously a string does not function as an operator.

local answer = num1 '+' num2
-- does not work

So is there anyway I can convert the string into its operator