25 into 20 best min fragment found: 15/2
  Cut up 25 sticks of length 20 like this:
    5 x (10 + 10)
    20 x (15/2 + 25/2)
  Reassemble as 20 sticks of length 25 like this:
    10 x (25/2 + 25/2)
    10 x (15/2 + 15/2 + 10)