Answer: The required percentage decrease is 9.1%.
Step-by-step explanation: Given that the price of a cup of coffee was $2.75 yesterday and today, the price fell to $2.50.
We are to find the percentage decrease and to round the answer to the nearest tenth of a percent.
We have
cost price of the cup of coffee yesterday = $2.75
and
cost of the cup of coffee today = $2.50.
So, the amount of decrease in the cup of coffee is

Therefore, the percentage decrease is given by

Rounding to the nearest tenth, we get
P = 9.1%.
Thus, the required percentage decrease is 9.1%.