Estimado ENTER:
No se supone que si usas el 2do ejemplo debiera ser algo así:
Private Sub Form_Load()
Dim Variacion, factorial1, factorial2 As Double
Dim n, k, i As Integer
n = CInt(15)
k = CInt(15 - 5)
factorial1 = n
factorial2 = k
For i = n - 1 To 1 Step -1
factorial1 = factorial1 * i
Next
For i = k - 1 To 1 Step -1
factorial2 = factorial2 * i
Next
Variacion = factorial1 / factorial2
Debug.Print Format(Variacion, "##,###")
End Sub
Lo que nos dá: 360.360 Variaciones
Saludos Cordiales