In this model, the producers hold 40000 kcal. Applying the ten percent rule at each transfer, about how much energy is available to the secondary consumers, which sit two transfers above the producers?

Explanation

Two transfers mean taking one tenth twice: 40000 kcal becomes 4000 kcal at the first consumer level and then 400 kcal at the second consumer level. The 4000 kcal choice stops after a single transfer and therefore answers for a level one step too low.