To convert a fraction to a percentage, we need to multiply it by 100. So, to find the percentage of 21/20, we can multiply it by 100.

21/20 x 100 = 105%

Therefore, 21/20 as a percentage is 105%. This means that if we have a whole object, and we divide it into 20 equal parts, then 21 of those parts would be equal to 105% of the whole object.