13.1. From 22 kg of fresh mushrooms, 2.5 kg of dried mushrooms are obtained, which still contain $12 \%$ water. What percentage of water is contained in fresh mushrooms?

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13.1. Let's find the mass of water contained in 2.5 kg of dry mushrooms. We get: $2.5 \cdot 12: 100=0.3$ kg. Therefore, the anhydrous mass is $2.5-0.3=2.2$ kg. This constitutes one-tenth of 22 kg, i.e., $10 \%$. Then, the remaining $90 \%$ is water.