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

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

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.