4 litres of water is mixed in certain amount of pure milk whose cost is Rs. 3 per litre. If the dishonest milkman earns a profit of 20% by selling the mixture at initial price then what is the quantity of pure milk obtained by the customer?
(a) 24
(b) 20
(c) 18
(d) 25
(e) None of these

• (b); Short Method: 4 litre≡20% of total amount
  or, 4×100/20≡total amount or, total amount=20 litre
  
• 7 years agoHelpfull: Yes(16) No(2)
• cost given = Rs 3/ltr.
  i.e cost earned through water mixture= 4*3 = 12 rs
  therefore earned 20%, that is on water .. therefore total earned = 12*100/20 = 60 rs.
  hence 60/3 = 20 ltr overall mixture!
• 7 years agoHelpfull: Yes(10) No(0)
• Answer
  let pure milk= x litr.
  total mixture=x+4
  3x*120/100=(x+4)3
  6x-5x=20
  x=20
• 7 years agoHelpfull: Yes(4) No(1)
• shortcut
  3 0
  
  3/1.2
  2.5 0.5
  
  5 1 substract along the diagonal
• 7 years agoHelpfull: Yes(2) No(3)
• 300(4+x)=3x*120
  x=20
• 7 years agoHelpfull: Yes(0) No(1)