gold is 19 times as heavy water and copper 9 in..., Ratio & Proportion, General Mathematics

Question:Gold is `19` times as heavy as water and copper is `9` times as heavy as water. In what ratio should these be mixed to get an alloy `15` times as heavy as water ?

A `1 : 1` 
B `2 : 3` 
C `1 : 2` 
D `3 : 2`

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+ AnswerD

+ ExplanationLet `1` gm of gold be mixed with `x` gm of copper to give 

`(1 + x)` gm of alloy.
 
Now, `1 G = 19 W, 1C = 9W & Alloy = 15 W`

`1` gm gold ` + x ` gm Copper `= (1 + x)`gm alloy.

`:. 19 W + 9 Wx = (1 + x) xx 15W`

or ` x = (4W)/(6W) = 2/3`.

So, the ratio of gold and copper is 

`1 : 2/3` or

`3 : 2`.

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