56. 180 g of gold with a fineness of 920 was alloyed with 100 g of gold with a fineness of 752. What is the fineness of the resulting alloy?
56. Assay of an alloy: $p=\frac{a}{b} \cdot 1000$, where $a$ is the weight of gold in the alloy, and $b$ is the weight of the alloy. That is: $p=\frac{100 \cdot 0.752 + 180 \cdot 0.920}{280} \cdot 1000=\frac{100 \cdot 752 + 180 \cdot 920}{280}=860$.