Question: how do you write 1/5 as a decimal?
Answer: What the divided sign is, is basically just a division sign. So, to get the decimal, you do 1÷5 .
This makes you get 0.2 . ... 
A percentage is a number over 100 .
To get 5 to 100 , you multiply it by 20 , and do the same for 1 , leaving you with 20100 .
So, your percentage is 20% .