Solution for number 14

First we label all the sacks with their number, 1, 2, etc.. to 10. Then, remove one pack from sack '1', two from sack '2', etc.. and take none from pack 10. You then weigh the 45 packs you have. If tey were all perfect (none lighter) than you should get 45 kg. If n of them are lighter, you will get 45-n*.1 kg. For example, if you weigh 44.6 kg, then you know that .4 kg are short, which means that you have 4 of the lighter sacks in the weighing. But, this means that pack number 4 is the lighter one.