Out of the total production of iron from hematite, an ore of Iron, 20% of the ore gets wasted, and out of the remaining iron, only 25% is pure iron. If the pure iron obtained in a year from a mine of hematite was 80,000 kg, then the quantity of hematite mined from that mine in the year is

Explanation:-

Let 100 kg of hematite be obtained then 20% of it get wasted that means 80 kg of ore remains.
Pure iron = 25% of remaining ore = 80*25/100 = 20 kg.
20 kg pure Iron is obtained from 100 of hematite.
1 kg pure Iron is obtained from = 100/20 hematite;
Then, 80000 kg pure Iron is obtained from = (100/20)*80000 = 400000 kg hematite.