A can contains a mixture of two liquids A and B is the ratio 7 : 5. When 9 litres of mixture are drawn off and the can is filled with B, the ratio of A and B becomes 7 : 9. How many litres of liquid A was contained by the can initially

• See the ratio of A = 7, check the options which are divisible by 7, 21 is there, simple tricky way.
• 8 years agoHelpfull: Yes(5) No(1)
• Suppose the can initially contains 7x and 5x litres of mixtures A and B respectively
  Quantity of A in mixture left
  = (7x - 7/12 x 9) litres = (7x - 21/4) litres.
  Quantity of B in mixture left
  = (5x - 5/12 x 9) litres = (5x - 15/4) litres.
  (7x - 21/4) / [(5x - 15/4)+9] = 7/9 = › 28x - 21/20x + 21 = 7/9 =› 252x - 189 = 140x + 147
  =› 112x = 336 =’ x = 3.
  So, the can contained 21 litres of A.
• 10 years agoHelpfull: Yes(4) No(3)
• Total mixer is x.
  A=7x/12 B=5x/12
  after drawn 9 lit of mixer........
  mixer remain(x-9)
  
  So the new ratio of A:B is ...
  A=7(x-9)/12 and B=5(x-9)/12
  now drawn 9 lit filled with B
  so B now contain B=5(x-9)/12 +9...........
  now the new ratio of mixer is A:B=7:9
  we know the new value of A and B...........put that in this equation
  
  7(x-9)/12:(5(x-9)/12+9)=7:9
  =>9x-81=5x-45+108
  =>x=36
  
  as known A=7x/12
  
  =>A=7*36/12
  =21
• 8 years agoHelpfull: Yes(4) No(2)