How many pounds of 10-6-4 fertilizer are needed to apply two pounds of actual nitrogen?

• A. 8 pounds
• B. 20 pounds
• C. 10 pounds
• D. 12 pounds

Answer: (B)

Fertilizer labels show the percentage of nitrogen by weight, so you use that to convert the desired nitrogen amount into fertilizer amount. A 10-6-4 label means 10% nitrogen. To get two pounds of actual nitrogen, you need enough fertilizer that 10% of its weight equals 2 pounds. Solve 0.10 × weight = 2, which gives weight = 2 / 0.10 = 20 pounds.

Check the reasoning: if you used 8 pounds, you’d get 0.8 pounds of N; 10 pounds would give 1 pound; 12 pounds would give 1.2 pounds. Only 20 pounds yields the required two pounds of nitrogen.