Gold is 19 times as heavy as water and copper 9 times as heavy as water. The ratio in which these two metals be mixed so that the mixture is 15 times as heavy as water is?

Let, 1 gm of gold be mixed with y gm of copper to give (1 +x) gm of mixture.
Now, 1G =19W and 1C = 9W and mixture = 15W
Now, 1 gm gold + y gm copper = (1 + y) gm mixture
∵ 19 W + 9W x y = (1 + y ) x 15W
Thus 4W = 6W x y
∴ y = 4W/6W = 4/6 = 2/3
So the required ratio is 1 : 2/3 i.e. 3 : 2