20% - think of it like this, you have 100 as a full percentage, to help, bring it down to 10. Now, you just have to figure out what 10/5 is, and that’s 2, so now you know you’re looking at intervals of 2, but since your real number is 100, we add a zero to the 2, making it 20, and putting this into a percentage!!
Hope this helps!!