The average age of A and B is 25 years. If A is to be replaced by C, the average would be 22 years. The average age of C and A is 19 years. The ages of A, B and C in order (in years) are:

22 , 28 , 16

 Average age of A and B is 25 years 

 A + B = 50 years        ----- ( 1) 

The average age of C and A is 19 years

  C + A = 38 years       ------ ( 2) 

 if A is replaced by C . then , average of B  and C is 22 years. 

  B +  C = 44 years       ------ ( 3 ) 

adding equation, 1 + 2 + 3 

   A+  B +  C = 66 years 

( A + B + C ) - ( A + B ) = 66 - 50  

 C= 16  years

( A + B + C ) - ( B + C ) = 66 - 44 

A =  22 years 

( A + B + C ) - ( A + C ) = 66 - 38 

 B = 28 years