arithmetic - copper is 7 times as heavy as water and gold is 13 times as heavy as water in what ratio should these be mixed to get an alloy 11 times as heavy as water - skillgun

Solution: C = 7W and G = 13W.
Let 1 gm of copper be mixed with x gm of gold to get (1+x)gm of alloy.
(1gm copper)+(xgm gold) = (x+1)gm of alloy.
=>7W+13W*x = (x+1)*11W
=> 7+13x = 11(x+1)
=> 2x = 4 => x = 2.
.'. Ratio of copper and gold = 1 : 2