Question

Gold is 19 times as heavy as water and copper is 9 times as heavy as water. In what ratio must these metals be mixed so that the mixture may be 12 times as heavy as water?
(a) 2:3
(b) 3:7
(c) 1:3
(d) 7:3
(e) None of these

Answer 1

G = 19W     gold is 19 times as heavy as water
C = 9W       copper is 9 times as heavy as water

 

Mixing A pounds of gold with B pounds of copper:
 A(G) + B(C) = 15W(A + B)
A(19W) + B(9W) = 15W(A + B)

divide both sides by W
19A + 9B = 15(A + B) 
19A + 9B = 15A + 15B 
4A = 6B 
A = (3/2) * B 

 for each part of Gold, there needs to be 1.5 parts Copper

 

Ratio Gold to copper:   1:1.5

not sure .....