The answer to the second question:

Take one coin from the 1st machine, 2 coins from the second machine, 3 coins from the third machine and so on. Measure the weight of the coins. If the obtained weight is one gram short of the expected result, 1st machine is producing defective coins, and if the obtained weight is two grams short of the expected result, then 2nd machine is producing defective coins.

For instance: if the weight of the coin is x, Then the expected result will be (1+2+....+10)x.