Question
A vessel is full of a mixture of kerosene and petrol in
which there is 18% kerosene, 8 litre are drawn off and then the vessel is filled with petrol. Resulting mixture has 15% of kerosene. How much does the vessel hold?Solution
Initial ratio = kerosene : Petrol = 18% : 82% = 9 : 41 Final ratio = kerosene : Petrol = 15% : 85% = 3 : 17 or 9 : 51 Difference in ratio due to 8 Ltr mixture drawn off and replaced by petrol. Initial ratio = kerosene : Petrol = 9 : 41 = 50 Final ratio = kerosene : Petrol = 9 : 51 = 60 ∴ Difference = 60 - 50 = 10 (Difference of 10 parts)/(Total parts (60)) So, 10/60  = 8 litre 1/6  = 8 litre Total = 8 × 6 = 48 litre.
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