Generating Random numbers that will sum to 1 specific value?

A set number of numbers, with a set minimum, set maximum and set total can not be random.

You have to lose at least one of these parameters in order to get random numbers.

Yes, it's easy enough to create pseudo-randoms within certain bounds, but it's very difficult if there isn't 'play' in at least one of the bounds, for example, a set of five random numbers from min 5 to max 10 which must total 50 leaves very few options.

This is not to be stubborn, but you've really got to let one of the bounds go to have a chance.

In terms of maths, depending on what you need to keep, solutions can be very simple, e.g.
10 random numbers (0 - 1) in A1:A10 then B1=A1*20000/sum(A$1:A$10) - each number is random, but the are normalised up such that the sum of the random numbers = 20000, but haven't fixed start or end points.

So, what could we lose?

See if this works for you:

Function RandTot(iTot As Long, iLo As Long, iHi As Long, _
                 Optional bVol As Boolean = False) As Variant
    Dim nNum        As Long
    Dim i           As Long
    Dim ad()        As Double
    Dim iTry        As Long

    If bVol Then Application.Volatile
    With Application.Caller
        If .Rows.Count > 1 And .Columns.Count > 1 Then
            RandTot = "Enter as row or column vector only!"
            Exit Function
        End If
        nNum = .Count
    End With

    If iHi < iLo Or _
       iTot < nNum * iLo Or _
       iHi > iTot Then
        RandTot = CVErr(xlErrValue)
        Exit Function
    End If

    ReDim ad(1 To nNum)
    Randomize

    With WorksheetFunction
        Do
            iTry = iTry + 1
            If iTry > 200 Then
                RandTot = "Time-out"
                Exit Function
            End If

            For i = 1 To nNum - 1
                ad(i) = RandBetw(iLo, iHi)
            Next i
            ad(i) = iTot - .Sum(ad) + ad(i)
        Loop Until .Min(ad) >= iLo And .Max(ad) <= iHi
    End With

    RandTot = ad
End Function

Function RandBetw(iLo, iHi) As Long
    RandBetw = (Rnd * (iHi - iLo) + Rnd * (iHi - iLo) + Rnd * (iHi - iLo)) / 4 + iLo
End Function

Copy the code to a Code module (see below), then select A1:A10 and use the formula,

=TRANSPOSE(RandTot(100000, 5000, 20000))

The formula MUST be confirmed with Ctrl+Shift+Enter rather than just Enter.

Adding a Macro to a Code Module
1. Copy the code from the post
2. Press Alt+F11 to open the Visual Basic Editor (VBE)
3. From the menu bar in the VBE window, do Insert > Module
4. Paste the code in the window that opens
5. Press Alt+Q to close the VBE and return to Excel

Populate 100 cells with what?

Hi.

It's a forum rule that you start your own thread, rather than try to "hijack" someone else's thread. This helps prevent massive confusion arising -which will happen if it is not clear which question is being answered. So please start your own thread and explain your own problem (make sure that, right from the start, you use a meaningful title (NOT things like "help needed" or "urgent problem"... think of the Google search terms that you would use to find the solution). Also, preferably attach an Excel sheet. Make sure there is enough data to demonstrate your need. Make sure your desired results are shown, mock them up manually if necessary. Remember to remove ALL confidential information first!!!

To attach a file:
Unfortunately the attachment icon doesn't work at the moment. So, to attach an Excel file you have to do the following: Just before posting, scroll down to Go Advanced and then scroll down to Manage Attachments. Now follow the instructions at the top of that screen.