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

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.

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.