A gallon of gasoline cost $3.09 two years ago. Now it costs $1.78. To the nearest percent, what has been the annual rate of decrease in cost?

Given that a gasoline was $3.09 two years ago and it goes for $1.78 now, the rate of decrease will be:

(Δ prices) / (time taken)

= (1.78-3.09) / 2

=-1.31/2

=-.655 dollars per year.

the answer is - 0.655 dollars per year