2 Answers

8.05 to 2.28   What is the percentage drop?
Divide 2.28 BY 8.05.  2.28 / 8.05 =  .2832,     Round to 100th place = .28
Now subtract .28 from 1.00 to find out what the drop was 1.00 - .28  =  .72 = 72%

The thing to remember is that a decimal can be easily changed to a percentage.  The decimal point is removed from the left and the percentage symbol is placed on the right.  
You only use the 10th and 100th places in the decimal to create the percentage.  Round up if you need (.2832 rounded to .28.     .2851 would round to .29)  
Examples:

.10  = 10%
.356 = 36% (round up)
.85 = 85%
1.25 = 125%

1.00 is 100%  (If you got 100% on a test, it means you got the whole one test correct.  1 whole test.  If the test had 100 questions and you answered 92 of them correctly, you earned 92/100 or .92 or 92%   If the test has some odd number of questions (15 for example) and you answer 11 of them correctly, you can find the percentage by dividing the amount correct by the number possible    11/15 = ..73 = 73%

The percentage decrease 8.05 to 2.28 is....................

Old  >  8.05             

New >  2.28              

                        8.05 / 100   =    2.28 / x   >  8.05x  =  228

                                                                       8.05         8.05

                                                                                x   =   28.32

28.32 - 100 =  -71.68 since it is a negative, take the absolute value. 71.68

The answer is 71.68%