How to convert 21/25 into 84% convert 17/20 into 85% what number over 30 equals 80%

To convert 21 out of 25 into 84% you have to divide 21 by 25 (calculator). But, if you're doing long division you do   25)¯2100 and you will still get 84%. 

And you do the same with 17/20  ---> 20)¯¯1700 and you will get 85%.

If you ever get a decimal just multiply it the number by 100 and you will get a percentage or you can just move the decimal to the right twice.

3. What number over 30 equals 80%?
 Set this up as N/30 = 80 (which is the same as saying what number over 30 equals 80%). 

N/30 = .80 
Multiply both sides by 30. 
The 30 will cancel out on the left side.
N = 24

Check it by dividing 24/30 = .80 --> 80%