VBA: How to create a function to divide the smallest number by the largest within a range

Hi, I'd like to know how to create a function by selecting a range (A1 to A30) and for the function to select the smallest number to divide by the largest one.
Example:
A1 50
A2 48
A3 45
A4 44
A5 40
A6 38
A7 30


I want my function to select A1 and A2 and divide A2 by A1 (48/50). I tried:

Function ratio(ByVal nb1 As Single, ByVal nb2 As Single) As Single
If nb2 > nb1 Then
  ratio = nb1 / nb2
Else
  Choose nb2 > nb1

End If
End function

It didn't work