A 20 kg metal bar made of alloy of tin and silver lost 2 kg of its weight in the water. 10 kg of tin loses 1.375 kg in the water; 5 kg of silver loses 0.375 kg. What is the ratio of tin to silver in the bar?
Choose the correct option:  A) 1 / 4  B) 2 / 5  C) 1 / 2  D) 3 / 5  E) 2 / 3

Rationale: "the bar lost certain percentage of its weight . we do n ' t know how much tin was lost and how much silver was lost but in all 2 kg was lost with is 10 % of its overall weight . tin loses 1.375 kg in 10 kg so 13.75 % of its weight when it is put in water . silver loses . 375 kg in 5 kg so . 375 / 5 * 100 = 7.5 % of its weight in water . now , we just need to use weighted averages : wt / ws = ( 7.5 - 10 ) / ( 10 - 13.75 ) = 2.5 / 3.75 = 2 / 3 answer ( e )"
Answer: E