In any food chain, the percentage of energy passed from one level to another usually reduced by a factor of 10%.
In the food chain given in the question, we are told that the rabbit ate grass and the hawk ate the rabbit.
The grass carried out photosynthesis and obtained 100% energy from the sun. When the rabbit ate the grass, he obtained 10% of the energy from the grass, thus, the quantity of energy it gained from eating the grass is 10%, that is, 100/10 = 10%.
When the hawk ate the rabbit, it was only able to get 10% of the energy in the rabbit, thus, the quantity of the energy it gained is 1%, that is 10/10 = 1%.
Therefore, 1% of the energy stored by the grass is passed on to the hawk.
