get one coin from machine 1, 2 from machine 2 3 from the 3rd and so forth. At the end you will have 55 coins to weigh.Wheght should be 550 gms. if all coins were normal.You should know what the weight of the defective coin is off by. i.e what is the difference between the good coin and the bad. Now take the total diff in weight and divide it by the diff in weght of one coin and you will get the machine that produces the bad coins
