Question

In 1950, the use of coal in the US was 114.6 million tons. The use of coal has decreased by 6.6% per year since then. Estimate the amount of coal used in the US in 2010. Round to the nearest tenth of a million tons.

Answer 1

The exponential function
   c(x) = 114.6×(1 -0.066)^x
evaluates to about 1.9 (million tons) for x = 60 years after 1950.

The amount of coal used in the US in 2010 is estimated at 1.9 million tons.