Question 68195
   
  
    Let sister's age  =  x
 
    So, Ricardo's age =  2x-4  (Given)
  
    The sum of the ages =  x + 2x - 4  =  20  (Given)
  
                        =  3x - 4  =  20
   
                        =  3x  =  20 + 4 = 24
  
                        =   x  =  24/3 =  8.
  
    So the sister's age =  8 yrs.
 and Ricardo's age  =  (2*8)-4 = 16-4  =  12 yrs.  Answer.