Anatural gas power plant is 60 efficient if one cubic meter of naturla gas provides 1000 btus os electricity. how manybtus of waste electricity is produced?

In energy production, possible sources are fossil fuels like coal, petroleum and natural gas. Other sources are renewable like hydro, solar and wind. Radioactive elements are also possible sources for nuclear energy. However, energy will always dissipate. Industries could never get 100% of the energy from their sources. In ideal cases like the Carnot engine, we can only get 60% of the energy. That is ideal. In actual, we get even lesser than this for about 40%. 

When the efficiency is 60%, the used energy is 60%, while the wasted energy is 40%. Therefore, the wasted energy is

1000 BTU (0.40) - 400 BTU

The waste energy in the form of electricity is 400 BTU.