In the morning a green-grocer puts 200 kg cucumbers outside in front of his shop. These cucumbers consists for 99% out of water. Because it is a warm day some water will evaporate. As a result, at the end of the day the cucumbers consist for 98% out of water. How many kg's of these cucumbers are left at the end of the day?

200 kg cucumbers consists for 99% out of water. From this statement it follows that 2 kg of the cucumbers consists of other material. At the end of the day part of the water is evaporated and the cucumbers consists for 98% out of water. Then this 2 kg other material which did not evaporate is 2 % of the total weight. Hence at the end of the day, the green-grocer has only 100 kg of cucumbers left.