Through common sense a number is already at it’s 100%. And so by increasing The percentage of the number you are also increasing the number itself.
For example take the number 10. If you increase it by 20% you'll take 2 out of 10 and add it to original number which will result in 12, 20% more or 120% in total. And so if you apply the same situation but with a hundred percent, you will double the number and get a number of 20 or 200%. An increase of a 100% plus the original 100%. If this doesn't make sense however, I'm sorry as my "explaining" skills suck
