achiever bio question

[msu08]

The ecological efficiency is only 5% from one trophic level to the next. For every 250 J of energy required by the secondary consumers, what is the minimum amount of energy the primary producers will have to generate?



A. 500 J
B. 5,000 J
C. 10,000 J
D. 100,000 J
E. 200,000 J

answer is D, they did 250/(.05)^2=100,000 J can anyone explain this? thanks!

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[Danny289]

The ecological efficiency is only 5% from one trophic level to the next. For every 250 J of energy required by the secondary consumers, what is the minimum amount of energy the primary producers will have to generate?



A. 500 J
B. 5,000 J
C. 10,000 J
D. 100,000 J
E. 200,000 J

answer is D, they did 250/(.05)^2=100,000 J can anyone explain this? thanks!

Primary producer ---------> first consumer--------> second counsumer
start backward you need 250 in Secondary with 5% (0.05) efficiacy
(X )0.05= 250
X=5000 you need in your primary consumar
(X)0.05=5000
X=100000 what you need in your primary producer or you approach this way:
(X)(0.05)^2=250
X= 100000