Finding the mean of a set of numbers

You never return a value in Add(), change x = ... to return ...

function Add()
	return First.Value + Second.Value + Third.Value + Fourth.Value + Fifth.Value
end

Also, be careful, if you call Add() before First, Second, etc, are defined, it'll error. It's better to define variables before functions.

Here's a rewritten version:

First = script.findMean.First
Second = script.findMean.Second
Third = script.findMean.Third
Fourth = script.findMean.Fourth
Fifth = script.findMean.Fifth
Plus = script.findMean.Plus

function Add()  
	return First.Value + Second.Value + Third.Value + Fourth.Value + Fifth.Value
end

--

First.Value = (math.random(1,10))
Second.Value = (math.random(1,10))
Third.Value = (math.random(1,10))
Fourth.Value = (math.random(1,10))
Fifth.Value = (math.random(1,10))

--

print(First.Value)
print(Second.Value)
print(Third.Value)
print(Fourth.Value)
print(Fifth.Value)

--

print("-")

Plus.Value = Add()
print(Plus.Value)

print("-")

print(Plus.Value / 5)

By the way, this really isn't a good way to do it. It's better to use a table rather than use a bunch of NumberValues.

Here's a simple way to get the average of numbers in a table:

local numbers = {23,5,2,12,10}

function average(table)
	local sum = 0
	for i = 1, #table do
		sum = sum + table[i]
	end
	return sum/#table
end

average(numbers) --> 10.4