How do you do questions like this: "16 is 5% of what number?"

16 = 5/100   times   x        where x is the number you want

16= 5x  /100

multiply both sides by  100

1600 = 5x

x= 1600/5

x= 320

Here is another take:

16 is to 5% as x is to 100%    then set it up as a ratio:

 

16/5% = x/100%                    Multiply both sides by 100%

 

16/5%  x 100% = x

16/5*100 = 320 = x