#14 Tomato Farmer

If you think, the solution to this one is easy, then you might be wrong.

At the start there are 99kg (99% of 100kg) water and 1kg (1% of 100kg) "other stuff". When the farmer arrived at the market, the percentage of water decreased to 98%. The weight of the "other stuff" stayed the same, but the percentage of the "other stuff" raised to 2% now. This means 2% = 1kg now and therefore 100% = 50kg. So the total weight of the tomatoes is 50kg now. This means, that 50kg water have evaporated.