four pieces: 1, 5, 10, and 10.. 1 = 1 2 = 1+1 3 = 1+1+1 ( you weigh 1 kg, take if out, weigh another, take it out, weigh the third one, and combine the three;)) ... 39 = 1+1+1+1+5+(10+10)+10 40 = (10+10) + (10+10) there you go.... it might now be the answer you were looking for.. but oh well... you can weight whatever you want with that now.... PROVE ME WRONG.... ahah