A 50 kg bag of fertiliser is labelled 3:2:1 (24). What mass of nitrogen does the bag contain?

1. The label carries two separate pieces of information and both are needed. 2. The number in brackets is the percentage by mass of the bag that is nitrogen, phosphorus and potassium together. 3. So 24 percent of the 50 kilogram bag is nutrient, which is 0.24 multiplied by 50. 4. That gives 12 kilograms of nutrient in the bag. 5. The three numbers before the bracket give the ratio in which that nutrient is split, in the order nitrogen, phosphorus, potassium. 6. Three plus two plus one is six parts in total, and nitrogen takes three of those parts. 7. Nitrogen is therefore three sixths, or one half, of the 12 kilograms, which is 6 kilograms. 8. The 12 kilogram answer is the trap for stopping at the total nutrient mass, the 4 kilogram answer splits the nutrient into three equal shares, and the 2 kilogram answer gives nitrogen the smallest share instead of the largest. _Source: Siyavula Physical Sciences Grade 12 (Everything Science, CC BY 4.0), Chapter 14: The chemical industry_