gold is 19 times as heavy as water and copper is 9 times as heavy as water in want ratio

Question

gold is 19 times as heavy as water and copper is 9 times as heavy as water in want ratio should these be mixed to get an alloy 15 times as heavy as water

 

please explain me

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