Thrice! First put seven gold bars on each side. If they are equal in weight, the one left out is the light one. If not, take the seven on the lighter side and put three on each side of the scale, if they are equal the one kept out will be lighter. If not, take the three on the lighter side and put one on each side and keep the third one out. You will easily realize which one is lighter on the scale, and if the scale is equal, then the one kept out is the lightest.
43. After 6 all numbers divisible by 3 can be ordered (because they can all be expressed as a sum of 6’s and 9’s). After 26, all numbers divisible by three when subtracted by 20 can be obtained. After 46, all numbers divisible by three when subtracted by 40 can be obtained. After 46, all numbers fit into one of these 3 categories, so all numbers can be obtained. 43 is the last number that doesn’t fall into one of these categories (44 = 20 + 6 * 4, 45 = 6 * 6 + 9).
Take four random men and set them aside. Now, weigh the remaining eight men on the seesaw, four on each side. One of the two things will happen.
1. The seesaw will balance perfectly. It means, that the light man is amongst the four men you set aside earlier. Use your second turn to weigh those four (two on each side) to see which side is heavier. At last, use your third and final seesaw turn to weigh those last two men to find the light man.
2. The seesaw will not balance perfectly. Now when you know that one of the four men on one side is light. Follow the steps just like scenario 1. above. Use your second turn to measure the four men, two on each side, then use your third and final seesaw turn to find out which of the man is lightweight.