Solution: Drink 40 grams of fresh bamboo juice for the first time, and there are 60 grams of fresh bamboo juice left. At this time, there is pure fresh bamboo juice (solute) in the bottle, 60× 80% = 48g, and it is filled with clear water. At this time, the solution is100g, and the solute is 48g, so the concentration is 48/100g = 48%.

I drank 40 grams of solution for the second time, leaving 60 grams of solution. At this time, there is 60×48%=28.8 grams of solute in the bottle, which is filled with clear water. At this time, the solution is 100g and the solute is 28.8g, so the concentration is 28.8/ 100=28.8%.

I drank 40 grams of solution for the third time, leaving 60 grams of solution. At this time, there is still 60× 28.8% =17.28g solute in the bottle, which is filled with clear water. At this time, the solution is100g and the solute is 17.28g, so the concentration is 17.28/65438.