Iron ore contains iron and impurities in a ratio of 7: 2. How many tons of iron will be obtained from 189 tons of ore?

To solve this problem, you need to write an equation. Let one part be x, then in iron ore iron is 7x, and impurities are 2x. Knowing that there are only 189 tons of ore, we calculate what one part is equal to.
7x + 2x = 189;
9 * x = 189;
x = 189/9;
x = 21.
Then the iron will turn out to be 21 * 7 = 147 tons.
Answer: 147 tons.