Efficiency is giving the minimum input to get results. A brief answer such as "relative density" to explain why oil floats on water is said to be an efficient answer. But it does not produce the intended result which is for the questioner to understand the concept, if one is not educated in the subject. The answer should be tailored to the level of understanding of the questioner. Efficiency which does not achieve the intent or objective, is pointless.
Student or Learner