What is the percent of decrease from 110 to 77

If you want to easily find the solution you can use your calculator.
Just divide 77 by 110 and see the result.
77/110 = 0.7 = 7/10 = 70/100 = 70% 
100% - 70% = 30%

Explanation
110*x=77
x=77/110, but the answer is not a percent
So 77/110 = ?/100  => ?=77*100/110=70 => 70%
But since 70% does not represent a percentage decreasement, we need to subtract it from the 100% 
100% - 70% = 30%