A vole eats 3,000 j of plant material. 1,600 j is indigestible and is eliminated as feces. 1,300 j are used in cellular respiration. what is the approximate production efficiency of this animal?

The answer is 3%.

What is left after feces is eliminated and the use in cellular respiration:

3,000 j - 1,600 j - 1,300 j = 100 j

Now, make a proportion.

3,000 j is 100%

100 j is x

3,000 j : 100% = 100 j : x

x = 100% * 100 j : 3,000 j

x = 3.33 % ≈ 3%