Question

Mark again the correct answer in each of the following:
An ore contains $$5\%$$ copper. How much ore is required to obtain $$400\ g$$ of copper?

Answer 1

Correct option is D. $$8\ kg$$
Because,
Assume $$x$$ be the required amount of ore.
$$=5\%$$ of $$x\ kg=0.4\ kg$$
$$=(5/100)\times x=0.4$$
$$=x=(0.4\times 100)/5$$
$$=x=40/5$$
$$=x=8\ kg$$