Two numbers are 20% and 25% less than a third number respectively. how much % is the second number less than the first number ?

Let A, B, C be three numbers.
Let B is 20% less than A , and C be 25%  less than A. 
 Let A be x, then
 B = x - 20% of x  = x - ( 20/100 )x  =  80x/100 = 0.8x           
C= x - 25% of x  =  x- 25/100x = 75x/100 = 0.75x
Now we have to find out how much %  C is less than B so 
            $$\begin{gathered} = (0.8x - 0.75x)/0.8x * 100 \\ = (0.05x/0.8x ) * 100 \\ = 100/16 \\ =6.25 \% \end{gathered}$$ 
               (answer)