Question 88717
Ricardo is 4 years less than twice as old as his sister. The sum of their age is 20. How old is Ricardo?
  
  Let the age of Ricardo be = x
  Let his sister's age be  = y
  sum of their ages is     = 20
  Also given Ricardo's age = 2(His sister's age)-4
                         x = 2y-4.....eq'n (1)
                       x+y = 20........eq'n(2)
     substituting for x in  eq'n (2)  we get 2y-4+y = 20
                                                  3y = 20+4 = 24  i.e, y =24/3
                                                  y = 8  
               substituting for y in eq'n (1) 
                                             x = 2(8)-4 = 16-4 = 12
       Ricardo's age is 12 yrs
      His sister's age is 8 yrs.