Question 4639
In these type of questions we are mainly concerned with three things.

Original Price   --  Increased Price  ---  Increase
 and the increase is given by :- Increase = Increased price - Original Price

Original Price   --  Decreased Price  ---  Decrease 
and the decrease is given by :- Decrease= Decreased price - Original Price

And the percentage for Increase or Decrease is given    by the FORMULA

(Increase/Original Price) * 100
OR 
(Decrease/Original Price) * 100

In both the cases we USE ORIGINAL PRICE 

NOw coming to the question --
Original Price =   $ 20
Increased Price =  $ 25
WHAT IS THE INCREASE ???    
YES IT IS $25 - $20 = $5
CAN YOU FIND THE PERCENTAGE NOW ??
IT IS ($5/$20)*100 = $500/$20 = 25%

HOPE IT IS CLEAR

If you need any help, you can contact me. I am avaliable for Online Tutoring also. Contact me on kapoorjai1@rediffmail.com