46 (1288). Freshly mined coal contains $2 \%$ water, and after two weeks of exposure to air, it contains $12 \%$ water. By how many kilograms has the mass of a ton of coal increased after the coal has been lying in the air for two weeks?
Solution. Since the freshly mined coal contains $2 \%$ water, in one ton of such coal, there are 20 kg of water and 980 kg of dry matter.

After two weeks of exposure to the air, the 980 kg of dry matter constitutes $88 \% (100 \% - 12 \% = 88 \%)$, meaning the total weight of the coal will be approximately 1114 kg $\left(\frac{980 \cdot 100}{88} \approx 1114\right)$.

Thus, the weight of the mined ton of coal has increased by about 114 kg.

Answer: by 114 kg.