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

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 = $$\frac{{80 \times 25}}{{100}} = 20\,{\text{kg}}$$
20 kg pure Iron is obtained from 100 of hematite
1 kg pure Iron is obtained from = $$\frac{{100}}{{20}}$$ hematite
Then, 80000 kg pure Iron is obtained from =$$\,\frac{{100}}{{20}} \times 80000 = \,$$    $$400000\,{\text{kg}}$$   hematite.