We can start by looking at it as a ratio, so 4 divided by 20 and 4/20 = 0.2, so that would be 20% viewing 1=100%.
Another way is
20 here is 100%, and for 20 to equal 100, we have to multiply it by 5. To balance it out, multiply the top by 5 as well, and 4 * 5 =20. Therefore, 4/20 = 20%
