In order to find the percent difference between two numbers first you need to find the difference between the two numbers. In this case the difference is 10
35-25=10
Next add take an average of the two numbers. Add them together and divide by the 2 to get the average.
25+35=60/2=30
Take the difference divided by the average
10/30=.3
Convert this to a percentage by moving the decmial place over 2 spots to the right. Add a 0 as a place older 30% difference.