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 10 times as heavy as water?

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 10 times as heavy as water?

Solution:
let, gold is 19x tme heavy and copper 9y times heavy as water

19x + 9y = 10 (x + y)
⇒ 19x + 9y = 10x + 10y
⇒ 19x - 10x = 10y - 9y
⇒ 9x = y
∴ x/y = 1/9
= 1 : 9