21 into 12 best min fragment found: 5
  Cut up 21 sticks of length 12 like this:
    3 x (6 + 6)
    18 x (5 + 7)
  Reassemble as 12 sticks of length 21 like this:
    6 x (7 + 7 + 7)
    6 x (5 + 5 + 5 + 6)