1. In $1000 \mathrm{~kg}$ of fresh plums, there is $77 \%$ water. After the evaporation of a certain amount of water, the mass of the plums was halved. What percentage of water do the plums now contain?
Solution. In $1000 \mathrm{~kg}$ of fresh mushrooms, there is $770 \mathrm{~kg}$ of water. After the evaporation of the water, the mass of the mushrooms was halved, which means that $500 \mathrm{~kg}$ of water evaporated. Therefore, in the remaining $500 \mathrm{~kg}$ of mushrooms, there is $770-500=$ $270 \mathrm{~kg}$ of water. This means that now the mushrooms contain $\frac{270}{500}=54 \%$ water.