Question

Suppose there are 500 units of energy available at the producer level of the energy pyramid. Approximately how many units of energy are available to the first-level consumer?
A. 100
B. 5
C. 50
D. 1

Answer 1

Your answer would be c. 50. Remember the 10% rule. Multiply 500 times .10 and get 50

Answer 2

B. 50 units of energy are available to the first-level consumers.

TERTIARY CONSUMERS             0.5
SECONDARY CONSUMERS        5 
PRIMARY CONSUMERS              50
PRODUCERS                            500

Every unit of energy available at the producer level decreases on every level raised. The unit of energy goes down by 10% in every level. Thus, when the energy from producers, 500 units, goes up to the first-level consumer or primary level, it energy becomes 50.