In 1 kg mixture of iron and manganese 20% of manganese. How much iron should be added so that
the proportion of manganese becomes 10%  Choose one
A) 1.5 kg B) 2 kg C) . 5 kg D) 1 kg E) none of these

Rationale: explanation : by the rule of alligation , we have percentage concentration of manganese in the mixture : 20 percentage concentration of manganese in pure iron : 0 percentage concentration of manganese in the final mixture 10 10 - 0 = 10 20 - 10 = 10 = > quantity of the mixture : quantity of iron = 10 : 10 = 1 : 1 given that quantity of the mixture = 1 kg hence quantity of iron to be added = 1 kg answer : option d
Answer: D