The ore contains 40% impurities, and the metal smelted from it contains 4% impurities.

The ore contains 40% impurities, and the metal smelted from it contains 4% impurities. How many tons of ore do you need to take to smelt 15 tons of metal from it?

1) If the proportion of impurities in the smelted metal is 4%, then the proportion of pure metal is 96%. We find the mass of metal with impurities:

15 t: 0.96 = 15 t 625 kg, is the mass of metal with impurities.

2) If the proportion of impurities in the ore is 40%, then the proportion of metal containing impurities is 60%. We find the mass of ore from which 15 tons of 625 kg of technical metal were extracted:

15 t 625 kg: 0.6 = 26 041 t 666 kg, is the mass of the ore.

Answer: to smelt 15 tons of pure metal, you need to extract 26,041 tons of 666 kg of ore.